Direct digital speaker apparatus having a desired directivity pattern

ABSTRACT

Direct digital speaker apparatus receiving a digital input signal and generating sound accordingly, the apparatus comprising an array of pressure-producing elements and a controller operative to compute a timing pattern determining if and when each pressure-producing element is actuated so as to achieve a desired directivity pattern.

REFERENCE TO CO-PENDING APPLICATIONS

Priority is claimed from U.S. provisional application No. 60/802,126filed 22 May 2006 and entitled “An apparatus for generating pressure”and from a U.S. provisional application No. 60/907,450 filed 2 Apr. 2007and entitled “Apparatus for generating pressure and methods ofmanufacture thereof” and from U.S. provisional application 60/924,203filed 3 May 2007 and entitled “Apparatus and Methods for GeneratingPressure Waves”.

FIELD OF THE INVENTION

The present invention relates generally to actuators and specifically tospeakers.

BACKGROUND OF THE INVENTION

The state of the art for actuators comprising an array of microactuators is believed to be represented by the following, all of whichare US patent documents unless otherwise indicated:

-   -   2002/0106093: The Abstract, FIGS. 1-42 and paragraphs 0009,        0023, and 0028 show electromagnetic radiation, actuators and        transducers and electrostatic devices.    -   U.S. Pat. No. 6,373,955: The Abstract and column 4, line        34-column 5, line 55 show an array of transducers.    -   JP 2001016675: The Abstract shows an array of acoustic output        transducers.    -   U.S. Pat. No. 6,963,654: The Abstract, FIGS. 1-3, 7-9 and column        7, line 41-column 8, line 54 show the transducer operation based        on an electromagnetic force.    -   U.S. Pat. No. 6,125,189: The Abstract; FIGS. 1-4 and column 4,        line 1-column 5, line 46, show an electro-acoustic transducing        unit including electrostatic driving.    -   WO 8400460: The Abstract shows an electromagnetic-acoustic        transducer having an array of magnets.    -   U.S. Pat. No. 4,337,379: The Abstract; column 3, lines 28-40,        and FIGS. 4, 9 show electromagnetic forces.    -   U.S. Pat. No. 4,515,997: The Abstract and column 4, lines 16-20,        show volume level.    -   U.S. Pat. No. 6,795,561: Column 7, lines 18-20, shows an array        of micro actuators.    -   U.S. Pat. No. 5,517,570: The Abstract shows mapping aural        phenomena to discrete, addressable sound pixels.    -   JP 57185790: The Abstract shows eliminating the need for a D/A        converter.    -   JP 51120710: The Abstract shows a digital speaker system which        does not require any D-A converter.    -   JP 09266599: The Abstract shows directly applying the digital        signal to a speaker.    -   U.S. Pat. No. 6,959,096: The Abstract and column 4, lines 50-63        show a plurality of transducers arranged within an array.

Methods for manufacturing polymer magnets are described in the followingpublications:

Lagorce, L. K. and M. G. Allen, “Magnetic and Mechanical Properties ofMicro-machined Strontium Ferrite/Polyimide Composites”, IEEE Journal ofMicro-electromechanical Systems, 6(4), December 1997; and

Lagorce, L. K., Brand, O. and M. G. Allen, “Magnetic micro actuatorsbased on polymer magnets”, IEEE Journal of Micro-electromechanicalSystems, 8(1), March 1999.

U.S. Pat. No. 4,337,379 to Nakaya describes a planar electrodynamicselectro-acoustic transducer including, in FIG. 4A, a coil-likestructure.

U.S. Pat. No. 6,963,654 to Sotme et al describes a diaphragm, flat-typeacoustic transducer and flat-type diaphragm. The Sotme system includes,in FIG. 7, a coil-like structure.

Semiconductor digital loudspeaker arrays are known, such as thosedescribed in United States Patent document 20010048123, U.S. Pat. No.6,403,995 to David Thomas, assigned to Texas Instruments and issued 11Jun. 2002, U.S. Pat. No. 4,194,095 to Sony, U.S. Pat. No. 4,515,997 toWalter Stinger, and Diamond Brett M., et al, “Digital soundreconstruction using array of CMOS-MEMS micro-speakers”, Transducers'03, The 12^(th) International Conference on Solid State Sensors,Actuators and Microsystems, Boston, June 8-12, 2003; and such as BBE'sDS48 Digital Loudspeaker Management System.

YSP 1000 is an example of a phased array speaker manufactured by Yamaha.

The disclosures of all publications and patent documents mentioned inthe specification, and of the publications and patent documents citedtherein directly or indirectly, are hereby incorporated by reference.

SUMMARY OF THE INVENTION

Provided herewith, in accordance with certain embodiments of the presentinvention, is direct digital speaker apparatus receiving a digital inputsignal and generating sound accordingly, the apparatus comprising anarray of pressure-producing elements such as but not limited to movingelements as described herein; and a controller operative to compute atiming pattern determining if and when each pressure-producing elementis actuated so as to achieve a desired directivity pattern.

Further in accordance with a preferred embodiment of the presentinvention, at least one pressure-producing element is capable ofproducing positive pressure pulses and at least one pressure-producingelement is capable of producing negative pressure pulses.

Still further in accordance with a preferred embodiment of the presentinvention, each pressure-producing element is operative to produce bothpositive pressure pulses and negative pressure pulses.

Also provided, in accordance with a preferred embodiment of the presentinvention, is a method for controlling direct digital speaker apparatusreceiving a digital input signal and generating sound accordingly, themethod comprising providing an array of pressure-producing elements, andcomputing a timing pattern determining if and when eachpressure-producing element is operative to produce pressure pulses so asto achieve a desired directivity pattern.

Further in accordance with a preferred embodiment of the presentinvention, each pressure-producing element comprises a moving element,operating to travel alternately back and forth along a respective path

Still further in accordance with a preferred embodiment of the presentinvention, the apparatus also comprises a user interface receiving adesired directivity pattern from a user.

Further in accordance with a preferred embodiment of the presentinvention, the directivity pattern is omni-directional defining a focalpoint.

Still further in accordance with a preferred embodiment of the presentinvention, the directivity pattern is cylindrical defining a focal axis.

Further in accordance with a preferred embodiment of the presentinvention, the directivity pattern is unidirectional defining an angleof propagation.

Still further in accordance with a preferred embodiment of the presentinvention, the directivity pattern comprises a combination of aplurality of unidirectional directivity patterns.

Further in accordance with a preferred embodiment of the presentinvention, the array is centered at the focal point.

Still further in accordance with a preferred embodiment of the presentinvention, the array is centered at a projection of the focal point.

Further in accordance with a preferred embodiment of the presentinvention, the array is oriented symmetrically relative to the axis.

Still further in accordance with a preferred embodiment of the presentinvention, the array is rectangular, defining four sides thereof, andthe four sides include two sides parallel to the axis.

Additionally in accordance with a preferred embodiment of the presentinvention, the timing pattern comprises employing a suitable delay forat least some of the pressure-producing elements, using the formula:delay=[(d²+r²)^(0.5)−d]/c, where r=distance between the projection ofthe focal point onto the pressure-producing elements array and a givenpressure-producing element, d=the distance of the plane of the array ofthe pressure-producing elements from the focal point of theomni-directional sound, and c=the speed of sound propagation through themedium in which the speaker is operating.

Still further in accordance with a preferred embodiment of the presentinvention, the timing pattern comprises employing a suitable delay forat least some of the pressure-producing elements, using the formula:delay=[(d²+r²)^(0.5)−d]/c, where r=distance between the projection ofthe focal axis onto the pressure-producing elements array and a givenpressure-producing element, e=the speed of sound through the medium inwhich the speaker is operating, and d=the distance of the plane of thearray of pressure-producing elements from the focal axis.

Further in accordance with a preferred embodiment of the presentinvention, the timing pattern comprises employing a suitable delay forat least some of the pressure-producing elements, using the formula:delay=x cos α where x=the distance from the plane defined by thepressure-producing elements array edge and a given pressure-producingelement and a=the angle between the direction of the uni-directionalpropagation and the pressure-producing elements array plane.

Further in accordance with a preferred embodiment of the presentinvention, each of the pressure-producing elements is individuallycontrolled.

Still further in accordance with a preferred embodiment of the presentinvention, the pressure-producing elements are moving elements, thatproduce pressure by virtue of their movement.

Still further in accordance with a preferred embodiment of the presentinvention, each moving element is responsive to alternating magneticfields and wherein the apparatus also comprises at least one latchoperative to selectively latch at least one subset of the movingelements in at least one latching position thereby to prevent theindividual moving elements from responding to the electromagnetic force,and wherein the controller comprises a magnetic field control systemoperative to receive the clock and, accordingly, to control applicationof the electromagnetic force to the array of moving elements; and alatch controller operative to receive the digital input signal and tocontrol the at least one latch accordingly.

Further in accordance with a preferred embodiment of the presentinvention, the method also comprises reading in a desired directivitypattern provided by a user.

Regarding terminology used herein:

Array: This term is intended to include any set of moving elements whoseaxes are preferably disposed in mutually parallel orientation and flushwith one another so as to define a surface which may be planar orcurved.

Above, Below: It is appreciated that the terms “above” and “below” andthe like are used herein assuming that, as illustrated by way ofexample, the direction of motion of the moving elements is up and downhowever this need not be the case and alternatively the moving elementsmay move along any desired axis such as a horizontal axis.

Actuator: This term is intended to include transducers and other devicesfor inter-conversion of energy forms. When the term transducers is used,this is merely by way of example and it is intended to refer to allsuitable actuators such as speakers, including loudspeakers.

Actuator element: This term is intended to include any “column” ofcomponents which, typically in conjunction with many other such columns,forms an actuator, each column typically including a moving element, apair of latches or “latching elements” therefor, each latching elementincluding one or more electrodes and insulative spacing materialseparating the moving element from the

Coil: It is appreciated that the alternating electromagnetic forceapplied to the array of moving elements in accordance with a preferredembodiment of the present invention may be generated by an alternatingelectric current oriented to produce a magnetic field gradient which isco-linear to the desired axes of motion of the moving elements. Thiselectric current may comprise current flowing through a suitablyoriented conductive coil or conductive element of any other suitableconfiguration. The term “coil” is used throughout the presentspecification as an example however it is appreciated that there is nointention to limit the invention which is intended to include allapparatus for applying an alternating electromagnetic force e.g. asdescribed above. When “coil” is used to indicate a conductor, it isappreciated that the conductor may have any suitable configuration suchas a circle or other closed figure or substantial portion thereof and isnot intended to be limited to configurations having multiple turns.

Channels, also termed “holes” or “tunnels”; These are illustrated asbeing cylindrical merely by way of example, this need not be the case.

Electrode: An electro-static latch. Includes either the bottom or topelectro-static latch which latches its corresponding moving element byvirtue of its being oppositely charged such that each latch and itsmoving element constitute a pair of oppositely charged electrodes.

Flexure: at least one flexible element on which an object is mounted,imparting at least one degree of freedom of motion to that object, forexample, one or more flexible thin or small elements peripheral to andtypically integrally formed e.g. from a single sheet of material, with acentral portion on which another object may or may not be mounted,thereby to impart at least one degree of freedom of motion to thecentral portion and objects mounted thereupon.

Latch, latching layer, latching mechanism: This term is intended toinclude any device for selectively locking one or more moving elementsinto a fixed position. Typically, “top” and “bottom” latching layers areprovided, which may be side by side and need not be one atop the other,and each latching layer includes one or many latching mechanisms whichmay or may not correspond in number to the number of moving elements tobe latched. The term “latch pair” is a pair of latches for an individualmoving element e.g. including a top latch and a bottom latch, which maybe side by side and need not be one atop the other.

Moving elements: These are intended to include any moving elements eachconstrained to travel alternately back and forth along an axis inresponse to an alternating electromagnetic force applied thereto. Movingelements are also termed herein “micro-speakers”, “pixels”,“micro-actuators”, “membranes” (individually or collectively) and“pistons”.

Spacers, also termed “space maintainers”: Include any element orelements mechanically maintaining the respective positions of theelectrodes and moving elements

The term “direct digital speaker” is used herein to include speakersthat accept a digital signal and translate the signal into sound waveswithout the use of a separate digital to analog converter. Such speakersmay sometime include an analog to digital converter as to allow them totranslate analog signals instead or in addition to digital signals. Suchspeakers may include DDS (Direct Digital Speakers), DDL (Direct DigitalLoudspeakers), DSR (Digital Sound Reconstruction) speakers, digitaluniform loudspeaker arrays, matrix speakers, and MEMS speakers. The term“direct digital speaker” as used herein is intended to include speakerapparatus having a multiplicity of pressure-producing elements, whichgenerate pressure either by virtue of their motion e.g. as specificallydescribed herein or by heating and cooling the medium in which theyreside, e.g. air, or by accelerating the medium in which they residee.g. by ionizing the medium and providing a potential difference alongan axis, or by operating as valves to selectively tap reservoirs ofmedium e.g. air, pressurized differently from the surroundingenvironment. The number of operating pressure producing elements (i.e.elements which are operating to generate pressure) is typically amonotonically increasing function of, e.g. proportional to, theintensity of the input signal, if analog, or to the digitally encodedintensity of the input signal, if digital.

The term “clock” used herein refers to the time duration associated witha single interval of the system clock.

The term “directivity pattern” as used herein refers to the pattern ofthe spatial distribution of the acoustic energy generated by speakerapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are illustrated in thefollowing drawings:

FIG. 1A is a simplified functional block diagram illustration ofactuator apparatus constructed and operative in accordance with apreferred embodiment of the present invention.

FIG. 1B is an isometric illustration of the array of moving elements ofFIG. 1A constructed and operative in accordance with a preferredembodiment of the present invention in which each moving elementcomprises a magnet and each is constrained to travel, except whenlatched, alternately back and forth along a respective axis in responseto an alternating electromagnetic force applied to the array of movingelements.

FIGS. 1C-1G are simplified top view illustrations of latches constructedand operative in accordance with five alternative embodiments of thepresent invention which can serve as alternatives to the latchspecifically shown in FIG. 1B.

FIG. 2A shows the array of FIG. 1B in a first, bottom extreme positionresponsive to an electromagnetic force applied downward.

FIG. 2B shows the array of FIG. 1B in a second, top extreme positionresponsive to an electromagnetic force applied upward.

FIG. 2C is similar to FIG. 2B except that one of the individual movingmagnets is not responding to the upward force because that individualmagnet is latched into its top extreme position by a correspondingelectric charge disposed above the individual moving magnet andfunctioning as a top latch.

FIGS. 3A-3C are respective top, cross-sectional and isometric views of askewed array of moving elements each constrained to travel alternatelyback and forth along a respective axis in response to an alternatingelectromagnetic force applied to the array of moving elements by a coilwrapped around the array.

FIG. 4A is an exploded view of an actuator device including an array ofmoving elements each constrained to travel alternately back and forthalong a respective axis in response to an alternating electromagneticforce applied to the array of moving elements by a coil, and a latch,formed as a layer, operative to selectively latch at least one subset ofthe moving elements in at least one latching position thereby to preventthe individual moving elements from responding to the electromagneticforce.

FIG. 4B is a simplified flowchart illustration of a preferred actuationmethod operative in accordance with a preferred embodiment of thepresent invention.

FIG. 5 is an isometric static view of the actuator device of FIG. 4Aconstructed and operative in accordance with a preferred embodiment ofthe present invention in which the array of moving elements is formed ofthin foil, each moving element being constrained by integrally formedflexures surrounding it.

FIG. 6A is an exploded view of a portion of the actuator device of FIG.5.

FIGS. 6B and 6C are a perspective view illustration and an explodedview, respectively, of an assembly of moving elements and associatedflexures, latches and spacer elements constructed and operative inaccordance with a preferred embodiment of the present invention whichreduces leakage of air through the flexures.

FIG. 6D is a cross-sectional view of the apparatus of FIGS. 6B-6Cshowing three moving elements in top extreme, bottom extreme andintermediate positions respectively.

FIG. 6E is a legend for FIG. 6D.

FIG. 7A is a static partial top view illustration of the moving elementlayer of FIGS. 5-6C.

FIG. 7B is a cross-sectional view of the moving element layer of FIGS.5-6 taken along the A-A axis shown in FIG. 7A.

FIG. 7C is a perspective view of the moving element layer of FIGS. 5-7Bwherein an individual moving element is shown moving upward toward itstop extreme position such that its flexures extend upward out of theplane of the thin foil.

FIG. 7D is a perspective view of a moving element layer constructed andoperative in accordance with an alternative embodiment of the presentinvention in which the disc-shaped permanent magnets of the embodimentof FIGS. 5-7C are replaced by ring-shaped permanent magnets.

FIG. 7E is a side view illustration of the flexure-restrained centralportion of an individual moving element in the embodiment of FIG. 7D.

FIG. 8A is a control diagram illustrating control of the latches and ofthe coil-induced electromagnetic force for a particular example in whichthe moving elements are arranged in groups that can each, selectively,be actuated collectively, wherein each latch in the latching layer isassociated with a permanent magnet, and wherein the poles of all of thepermanent magnets in the latching layer are all identically disposed.

FIG. 8B is a flowchart illustrating a preferred method whereby alatching controller may process an incoming input signal and controlmoving elements' latches accordingly, in groups.

FIG. 8C is a simplified functional block diagram illustration of aprocessor, such as the processor 802 of FIG. 8A, which is useful incontrolling substantially any of the actuator devices with electrostaticlatch mechanisms shown and described herein.

FIG. 8D is a simplified flowchart illustration of a preferred method forinitializing the apparatus of FIGS. 1-8C.

FIG. 8E is a simplified isometric view illustration of an assembledspeaker system constructed and operative in accordance with a preferredembodiment of the present invention.

FIG. 8F is a simplified flowchart illustration of a preferred method ofoperation for generating a sound using apparatus constructed andoperative in accordance with an embodiment of the present invention.

FIG. 9A is a graph summarizing certain, although typically not all, ofthe forces brought to bear on moving elements in accordance with apreferred embodiment of the present invention.

FIG. 9B is a simplified pictorial illustration of a magnetic fieldgradient inducing layer constructed and operative in accordance with apreferred embodiment of the present invention.

FIGS. 9C-9D illustrate the magnetic field gradient induction function ofthe conductive layer of FIG. 9B.

FIG. 10A is a simplified top cross-sectional illustration of a latchinglayer suitable for latching moving elements partitioned into severalgroups characterized in that any number of moving elements may beactuated by collectively actuating selected groups from among thepartitioned groups, each latch in the latching layer being associatedwith a permanent magnet, wherein the poles of all of the permanentmagnets in the latching layer are all identically disposed.

FIG. 10B is a simplified electronic diagram of an alternative embodimentof the latch layer of FIGS. 1-10A in which each latch is individuallycontrolled by the latching controller 50 of FIG. 8C. It is appreciatedthat the latches are shown to be annular however alternatively may haveany other suitable configuration as described herein. The layer of FIG.108 comprises a grid of vertical and horizontal wires definingjunctions. A gate such as a field-effect transistor is typicallyprovided at each junction. To open an individual gate thereby to chargethe corresponding latch, voltage is provided along the correspondingvertical and horizontal wires.

FIG. 11A is a timing diagram showing a preferred control scheme used bythe latch controller in uni-directional speaker applications wherein aninput signal representing a desired sound is received, and movingelements constructed and operative in accordance with a preferredembodiment of the present invention are controlled responsively, so asto obtain a sound pattern in which the volume in front of the speaker isgreater than in other areas, each latch in the latching layer beingassociated with a permanent magnet, and the poles of all of thepermanent magnets in the latching layer preferably all or substantiallyall being similarly or identically disposed.

FIG. 11B is a schematic illustration of an example array of movingelements to which the timing diagram of FIG. 11A pertains.

FIG. 11C is a timing diagram showing a preferred control scheme used bythe latch controller in omni-directional speaker applications wherein aninput signal representing a desired sound is received, and movingelements constructed and operative in accordance with a preferredembodiment of the present invention are controlled responsively, so asto obtain a sound pattern in which the volume in front of the speaker issimilar to the volume in all other areas surrounding the speaker.

FIGS. 12A and 1213 are respectively simplified top view andcross-sectional view illustrations of the moving element layer inaccordance with an alternative embodiment in which half of the permanentmagnets are placed north pole upward and half north pole downward.

FIG. 13 is a simplified top view illustration similar to FIG. 10A exceptthat half of the permanent magnets in the latching layer are disposednorth pole upward and the remaining half of the permanent magnets in thelatching layer are disposed north pole downward.

FIG. 14 is a control diagram illustrating control of the latches and ofthe coil-induced electromagnetic force for a particular example in whichthe moving elements are arranged in groups that can each, selectively,be actuated collectively, similar to FIG. 8A except that half of thepermanent magnets in the latching layer are disposed north pole upwardand the remaining half of the permanent magnets in the latching layerare disposed north pole downward.

FIG. 15A is a timing diagram showing a preferred control scheme used bythe latch controller in uni-directional speaker applications, which issimilar to the timing diagram of FIG. 11A except that half of thepermanent magnets in the latching layer are disposed north pole upwardand the remaining half of the permanent magnets in the latching layerare disposed north pole downward.

FIG. 15B is a schematic illustration of an example array of movingelements to which the timing diagram of FIG. 15A pertains.

FIG. 15C is a graph showing changes in the number of moving elementsdisposed in top and bottom extreme positions at different times and as afunction of the frequency of the input signal received by the latchingcontroller of FIG. 8C.

FIG. 16A illustrates a moving element layer which is an alternative tothe moving element layer shown in FIGS. 1A and 2A-2C in which the layeris formed from a thin foil such that each moving element comprises acentral portion and surrounding portions.

FIG. 16B is still another alternative to the moving element layer shownin FIGS. 1A and 2A-2C in which a sheet of flexible material e.g. rubbercapable of enabling motion i.e. there are rigid discs under the magnet.the magnet might be the rigid element but it might not be rigid enough.

FIG. 16C is an isometric view of a preferred embodiment of the movingelements and surrounding flexures depicted in FIG. 7A-7E or 16A in whichflexures vary in thickness.

FIG. 16D is an isometric illustration of a cost effective alternative tothe apparatus of FIG. 16C in which flexures vary in width.

FIG. 17 is a top cross-sectional view illustration of an array ofactuator elements similar to the array of FIG. 3A except that whereas inFIG. 3A, consecutive rows of individual moving elements or latches arerespectively skewed so as to increase the number of actuator elementsthat can be packed into a given area, the rows in FIG. 17 are unskewedand typically comprise a rectangular array.

FIG. 18 is an exploded view of an alternative embodiment of an array ofactuator elements in which the cross-section of each actuator element issquare rather than round.

FIG. 19 is an isometric array of actuators supported within a supportframe providing an active area which is the sum of the active areas ofthe individual actuator arrays.

FIG. 20A is a simplified generally self-explanatory functional blockdiagram illustration of a preferred system for achieving a desireddirectivity pattern for a desired sound stream using a direct digitalspeaker with characteristics as indicated in the drawing, such as thatshown and described herein in FIGS. 1A-19.

FIG. 20B is a simplified generally self-explanatory functional blockdiagram illustration of a preferred system for achieving a desireddirectivity pattern for a desired sound stream which is of generalapplicability in that it need not employ a direct digital speaker withcharacteristics as indicated in FIG. 20A e.g. that shown and describedherein in FIGS. 1A-19 and may instead employ any suitable direct digitalspeaker.

FIG. 21 is a simplified flowchart illustration of per-clock operation ofthe moving element constraint controller 3050 of FIG. 20, in accordancewith certain embodiments of the present invention.

FIG. 22A is a simplified diagram of an omni-directional propagationpattern.

FIG. 22B is a diagram of a preferred positioning of a moving elementarray relative to the focal point of the desired omni-directional soundpropagation pattern of FIG. 22A.

FIG. 23 is a simplified pictorial illustration of speaker apparatusconstructed and operative in accordance with FIGS. 20A-22B andoperative, e.g. by virtue of having been so programmed, to generateomni-directional sound which is particularly suitable for an environmentin which consumers of the sound entirely surround the speaker, typicallyat more than one levels including a ground level and a first floor levelas shown.

FIG. 24 is a diagram of a cylindrical pattern of sound directivity whichit is achievable using an embodiment of the apparatus of the presentinvention.

FIG. 25 is a diagram showing one preferred positioning of the movingelement array 3010, shown to be rectangular by way of example, relativeto the cylindrical pattern of sound directivity shown in FIG. 24.

FIG. 26 is an isometric view of the moving element array of FIGS.20A-20B, showing uni-directional sound generated by that moving arrayand propagating in a desired or predetermined direction a as indicatedby arrows.

FIG. 27 is a pictorial illustration of a preferred application forspeaker apparatus 3600 constructed and operative in accordance with thepresent invention, being constructed e.g. programmed to generateuni-directional sound in at least one typically user-selected direction.

FIG. 28 is a simplified pictorial illustration of a non-rectangulararray of moving elements constructed and operative in accordance with apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The technical field of the invention is that of a digital transducerarray of long-stroke electromechanical micro actuators constructed usingfabrication materials and techniques to produce low cost devices for awide variety of applications, such as audio speakers, biomedicaldispensing applications, medical and industrial sensing systems, opticalswitching, light reflection for display systems and any otherapplication that requires or can derive benefit from longer-travelactuation and/or the displacement of greater volumes of fluid e.g. airor liquid relative to the transducer size.

A preferred embodiment of the present invention seeks to provide atransducer structure, a digital control mechanism and variousfabrication techniques to create transducer arrays with a number, N, ofmicro actuators. The array is typically constructed out of a structureof typically three primary layers which in certain embodiments wouldcomprise of a membrane layer fabricated out of a material of particularlow-fatigue properties that has typically been layered on both sideswith particular polar aligned magnetic coatings and etched with anumber, N, of unique “serpentine like” shapes, so as to enable portionsof the membrane bidirectional linear freedom of movement (the actuator).The bidirectional linear travel of each moving section of the membraneis confined within a chamber (actuator channels) naturally formedtypically by sandwiching the membrane layer between two mirror imagesupport structures constructed out of dielectric, Silicon, Polymer orany other like insulating substrate, are typically fabricated with Nprecisely sized through holes equal in number to the N serpentineetchings of the membrane and typically precisely positioned in a patternwhich precisely aligns each through hole with each serpentine etching ofthe membrane. Further affixed to the outer surfaces of both the top andbottom layers of the support structure are, typically, conductiveoverhanging surfaces such as conductive rings or discs (“addressableelectrodes”), which serve to attract and hold each actuator as itreaches its end of stroke typically by applying electrostatic charge.

A device constructed and operative in accordance with a preferredembodiment of the present invention is now described with reference toFIGS. 1B, 2A-2C, 3A-3C, to 4A, 5, 6A, 7A-7B, 8A-8B, 9, 10A, 11A, 12A,13, 14, 15A, 16A-C, 17-19.

FIG. 1B is a conceptual overview of a small section of the device. FIG.2A depicts the movement of the moving elements under magnetic field.FIG. 2B depicts the movement of the same moving elements under anopposite magnetic field. FIG. 2C depicts the movement of the movingelements under a magnetic field while one is electrode is charged. FIGS.3A-3C are respective top, cross-sectional and perspective views of onepreferred embodiment of the present invention.

FIG. 4A is an exploded view of a device constructed and operative inaccordance with a preferred embodiment of the present invention. FIG. 5is a detailed illustration of a small section of the device constructedand operative in accordance with a preferred embodiment of the presentinvention. FIG. 6A is an exploded view of the same small section. FIG.7A is a pictorial illustration of a serpentine and moving elementssubassembly constructed and operative in accordance with a preferredembodiment of the present invention. FIG. 7B is an illustrative view ofa single element, constructed and operative in accordance with apreferred embodiment of the present invention, in motion. FIG. 8A is ablock diagram of a speaker system constructed and operative inaccordance with a preferred embodiment of the present invention. FIG. 8Bis a flow diagram of the speaker system constructed and operative inaccordance with a preferred embodiment of the present invention. FIG. 9Aillustrates a preferred relationship between the different forcesapplied to the moving elements.

FIG. 10A is a grouping view of the electrodes constructed and operativein accordance with a preferred embodiment of the present invention. FIG.11A is a timing and control chart constructed and operative inaccordance with a preferred embodiment of the present invention. FIG.12A illustrates magnetic properties of moving elements for analternative addressing embodiment. FIG. 13 illustrates grouping ofelectrodes in an alternative addressing embodiment. FIG. 14 is asimplified block diagram of the speaker system in an alternativeaddressing embodiment. FIG. 15A is a timing and control chart for analternative embodiment. FIG. 16A is a small section of the movingelements subassembly constructed and operative in accordance with apreferred embodiment of the present invention. FIG. 16B is a smallsection of a different embodiment of the moving elements subassembly,using a flexible substrate constructed and operative in accordance witha preferred embodiment of the present invention.

Whereas FIGS. 3A-3C above illustrate an array of elements in a honeycombconstruction constructed and operative in accordance with a preferredembodiment of the present invention, FIG. 17 illustrates an array ofelements in a square construction, which is constructed and operative inaccordance with a preferred embodiment of the present invention. FIG. 18is an exploded view of a small section of an embodiment using squareshaped elements. FIG. 19 illustrates an apparatus using a plurality(array) of devices.

Effective addressing is typically achieved through unique patterns ofinterconnects between select electrodes and unique signal processingalgorithms which typically effectively segments the total number ofactuators in a single transducer, into N addressable actuator groups ofdifferent sizes, beginning with a group of one actuator followed by agroup of double the number of actuators of its previous group, until allN actuators in the transducer have been so grouped.

To attain actuator strokes the transducer is typically encompassed witha wire coil, which, when electrical current is applied, creates anelectromagnetic field across the entire transducer. The electromagneticfield causes the moving part of the membrane to move typically in alinear fashion through the actuator channels. If the current alternatesits polarity, it causes the moving part of the membrane to vibrate. Whenelectrostatic charge is applied to particular addressable electrodegroups, it will typically cause all actuators in that group to lock atthe end of the stroke, either on top or bottom of the support structurein accordance with the application requirement. Collectively thedisplacement provided by the transducer is achieved from the sum totalof the N actuators that are not locked at any particular interval (superposition).

The transducer construction is typically fully scalable in the number ofactuators per transducer, the size of each actuator, and the length ofstroke of each actuator, and the number of addressable actuator groups.In certain embodiments, the actuator elements may be constructed byetching various shapes into a particular material, or by using layeredmetallic disks that have been coated with a flexible material or byusing free floating actuator elements The membrane (flexure) materialsmay include Silicon, Beryllium Copper, Copper Tungsten alloys, CopperTitanium alloys, stainless steel or any other low fatigue material. Theaddressable electrodes of the support structure may be grouped in anypattern as to attain addressing as appropriate for the transducerapplication. The addressable electrodes may be affixed such that contactis created with the membrane actuator or in such a manner that there isno physical contact with the membrane. The substrate material may be ofany insulating material such as FR4, silicon, ceramic or any variety ofplastics. In some embodiments the material may contain ferriteparticles. The number of serpentine shapes etched into the membrane, orfloating actuator elements and the corresponding channels of the supportstructure may be round, square or any other shape. The electromagneticfield may be created by winding a coil around the entire transducer,around sections of the transducer or around each actuator element or byplacing one or more coils placed next to one or more actuator elements.

In certain embodiments a direct digital method is used to produce soundusing an array of micro-speakers. Digital sound reconstruction typicallyinvolves the summation of discrete acoustic pulses of energy to producesound-waves. These pulses may be based on a digital signal coming fromaudio electronics or digital media in which each signal bit controls agroup of micro-speakers. In one preferred embodiment of the currentinvention, the nth bit of the incoming digital signal controls 2^(n)micro-speakers in the array, where the most significant bit (MSB)controls about half of the micro-speakers and the least significant bit(LSB) controls at least a single micro-speaker. When the signal for aparticular bit is high, all of the speakers in the group assigned to thebit are typically activated for that sample interval. The number ofspeakers in the array and the pulse frequency determine the resolutionof the resulting sound-wave. In a typical embodiment, the pulsefrequency may be the source-sampling rate. Through the post applicationof an acoustic low-pass filter from the human ear or other source, thelistener typically hears an acoustically smoother signal identical tothe original analog waveform represented by the digital signal.

According to the sound reconstruction method described herein, thegenerated sound pressure is proportional to the number of operatingspeakers. Different frequencies are produced by varying the number ofspeaker pulses over time. Unlike analog speakers, individualmicro-speakers typically operate in a non-linear region to maximizedynamic range while still being able to produce low frequency sounds.The net linearity of the array typically results from linearity of theacoustic wave equation and uniformity between individual speakers. Thetotal number of non-linear components in the generated sound wave istypically inversely related to the number of micro-speakers in thedevice.

In a preferred embodiment a digital transducer array is employed toimplement true, direct digital sound reconstruction. The producedsound's dynamic range is proportional to the number of micro-speakers inthe array. The maximal sound pressure is proportional to the stroke ofeach micro-speaker. It is therefore desirable to generate long stroketransducers and to use as many as possible. Several digital transducerarray devices have been developed over the years. One worth mentioningis a CMOS-MEMS micro-speaker developed at Carnegie Mellon University.Using CMOS fabrication process, they designed an 8-bit digital speakerchip with 255 square micro-speakers, each micro-speaker 216 μm on aside. The membrane is composed of a serpentine Al—SiO2 mesh coated withpolymer and can be electrostatically actuated by applying a varyingelectrical potential between the CMOS metal stack and silicon substrate.The resulting out of plane motion is the source of pressure waves thatproduce sound. Each membrane has a stroke of about 10 μm. Such shortstrokes are insufficient and the generated sound levels are too soft fora loudspeaker. Another issue is that the device requires a drivingvoltage of 40V. Such voltage requires complex and expensive switchingelectronics. Preferred embodiments of the device described hereinovercome some or all of these limitations and generate much louder soundlevels while eliminating the need for high switching voltages.

It is believed that the shape of each transducer has no significanteffect on the acoustic performance of the speaker. Transducers may bepacked in square, triangle or hexagonal grids, inter alia.

The current invention typically makes use of a combination of magneticand electrostatic forces to allow a long stroke while avoiding theproblems associated with traditional magnetic or electrostaticactuators.

The moving elements of the transducer array are typically made toconduct electricity and may be magnetized so that the magnetic poles areperpendicular to the transducer array surface. Moderate conduction issufficient. A coil surrounds the entire transducer array or is placednext to each element and generates the actuation force. Applyingalternating current or alternating current pulses to the coil creates analternating magnetic field gradient that forces all the moving elementsto move up and down at the same frequency as the alternating current. Tocontrol each moving element, two electrodes may be employed, one aboveand one below the moving elements.

The current applied to the coil typically drives the moving elementsinto close proximity with the top and bottom electrode in turn. A smallelectrostatic charge is applied to the moving elements. Applying anopposite charge to one of the electrodes generates an attracting forcebetween the moving element and the electrode. When the moving element isvery close to the electrode, the attracting force typically becomeslarger than the force generated by the coil magnetic field and theretracting spring and the moving element is latched to the electrode.Removing the charge or some of it from the electrode typically allowsthe moving element to move along with all the other moving elements,under the influence of the coil magnetic field and the flexures.

In accordance with certain embodiments, the actuator array may bemanufactured from 5 plates or layers:

-   -   Top electrode layer    -   Top spacers (together shown as layer 402)    -   Moving elements 403    -   Bottom spacers    -   Bottom electrode layer (together shown as layer 404)

In accordance with certain embodiments, the array is surrounded by alarge coil 401. The diameter of this coil is typically much larger thanthat of traditional coils used in prior art magnetic actuators. The coilcan be manufactured using conventional production methods.

In certain embodiments the moving element is made of a conductive andmagnetic material. Moderate electrical conduction is typicallysufficient. The moving element may be manufactured using many types ofmaterials, including but not limited to rubber, silicon, or metals andtheir alloys. If the material cannot be magnetized or a stronger magnetis desired, a magnet may be attached to it or it may be coated withmagnetic material. This coating is typically done by application, usinga screen printing process or other techniques known in the art, by epoxyor another resin loaded with magnetic powder. In some embodiments,screen printing can be performed using a resin mask created through aphoto-lithographic process. This layer is typically removed after curingthe resin/magnetic powder matrix. In certain embodiments the epoxy orresin is cured while the device is subjected to a strong magnetic field,orienting the powder particles in the resin matrix to the desireddirection. The geometry of the moving elements can vary. In yet otherembodiments, part of the moving elements may be coated with the magnetand cured with a magnetic field oriented in one direction while the restare coated later and cured in an opposite magnetic field causing theelements to move in opposite directions under the same external magneticfield. In one preferred embodiment, the moving element comprises a platethat has a serpentine shape surrounding it, typically cut out from thinfoil. Alternatively, in certain embodiments it is possible to use athick material thinned only in the flexure area or by bonding relativelythick plates to a thin layer patterned as flexures. This shape allowspart of the foil to move while the serpentine shape serves as acompliant flexure. In certain other embodiments, the moving part is acylinder or a sphere, free to move about between the top and bottomelectrodes.

FIG. 1B, which illustrates a conceptual overview of small section of thedevice in accordance with certain embodiments of the invention, servesto provide a conception overview of the complete transducer arraystructure. In the illustrated embodiment the moving elements are pistons101 which are typically magnetized so that one pole 102 is on the topand the other 103 at the bottom of each piston. A magnetic fieldgenerator (not shown) that typically influences the entire transducerarray structure creates a magnetic field across the entire transducerarray, typically causing pistons 101 to move up and down, therebyforcing the air out of the cavity 104. An electrostatic electrodetypically resides on both the top 105 and bottom 106 of each cavity. Theelectrodes serve as latching mechanisms that attract and hold eachpiston as it nears its end of stroke typically preventing the pistonfrom moving until the latch is released, while allowing the pushed airto easily pass through. In certain embodiments, the pistons 101 are madeof an electrically conductive material or coated with such material. Atleast one of the elements, the piston and/or the electrostatic electrodeis typically covered by an dielectric layer to avoid shorting aspull-down occurs.

FIGS. 2A-2C, taken together, illustrate the element movement accordingto a preferred embodiment of the present invention. In this embodiment acoil (not shown) typically surrounds the entire transducer arraystructure, creating a magnetic field across the entire transducer arraywhich causes any magnetic element with freedom of movement to travelaccording to the alternating direction of the field. This causes thepistons to move typically up and down.

In FIG. 2A the magnetic field 201 direction is downwards. The magneticfield creates a force, driving the pistons 101 of the entire arraydownwards.

In FIG. 2B the magnetic field 202 direction has changed and is pointingupwards. The magnetic field creates a force, driving the pistons 101 ofthe entire array upwards.

In FIG. 2C a positive electric charge is applied to one of the topelectrodes 205. The positive charge typically attracts the electrons inthe piston 204, causing the top of the piston 206 to be negativelycharged. The opposite charges 205 and 206 create an attraction forcewhich, when the gap is below a critical distance, typically act topull-down the two elements together. The magnetic field 203 directionhas changed again and is pointing downwards. The piston 204 is typicallyheld in place due to magnetic attraction while the rest of the pistonsare free to move, and move to the bottom due to the influence of themagnetic field 203. In this particular embodiment the charge applied tothe electrode is positive. Alternatively, a negative charge may beapplied to the electrodes, which will induct a negative charge toaccumulate in the near-side of the adjacent piston.

FIGS. 3A-3C show top, cross-sectional and perspective views of onepreferred embodiment.

In certain embodiments a coil 304 wrapped around the entire transducerarray generates an electromagnetic field across the entire arraystructure, so that when current is applied, the electromagnetic fieldcauses the pistons 302 to move up 301 and down 303.

FIG. 4A shows an exploded view of the device constructed and operativein accordance with certain embodiments of the invention. As shown, theexploded view of a transducer array structure reveals that it comprisesthe following primary parts:

(a) A coil surrounding the entire transducer array 401 generates anelectromagnetic field across the entire array structure when voltage isapplied to it. A preferred embodiment for the coil is described hereinwith reference to FIGS. 9B-9D.

(b) In certain embodiments a top layer construction 402 may comprise aspacer layer and electrode layer. In a certain embodiment this layer maycomprise a printed circuit board (herein after “PCB”) layer with anarray of accurately spaced cavities each typically having an electrodering affixed at the top of each cavity.

(c) The moving elements (“pistons”) 403 in the current embodiment may becomprised of a thin foil of conductive magnetized material cut or etchedwith many very accurate plates typically surrounded by “serpentine”shapes that serve as compliant flexures that impart the foils with aspecific measure of freedom of movement.

(d) A bottom layer construction 404 may comprise a spacer layer andelectrode layer. In a certain embodiment this layer may comprise adielectric layer with an array of accurately spaced cavities eachtypically having an electrode ring affixed at the bottom of each cavity.

FIG. 5 shows details of a small section of a device constructed andoperative in accordance with a preferred embodiment of the presentinvention. A cross section detailed dimensional view of the transducerarray according to the illustrated embodiment shows the followingstructure: the moving elements (“pistons”), typically made from a thinfoil 501 that has been cut or etched into precise plate and serpentineshapes having a magnetized layer on the top 502 and bottom 503, isaccurately positioned so the center of each plate shape is preciselyaligned with the center of each of the cavities of a top layerdielectric 504 and the bottom layer dielectric cavity 505 thatcollectively serve as travel guides and air ducts. At the external edgesof each duct both on the top 506 and on the bottom 507 is a copper ring(“electrode”) latching mechanism which, when electrostatic charge isapplied, typically attracts each moving element to create contactbetween the moving elements (“pistons”) and latches and holds eachmoving element (“piston”) as it nears the end of each stroke, therebypreventing the moving element (“piston”) from moving until the latch isreleased typically by terminating the electrostatic charge to theelectrode.

FIG. 6A shows an exploded view of the same small section as shown inFIG. 5. and reveals that in this embodiment the thin foil which has beenetched with precise serpentine shapes to create a moving element(“piston”) with the center of each shape affixed with a magnetized layeron the top and bottom, is centered and enclosed in the cavities ofmirror image on the top 602 and bottom 603 dielectric.

FIG. 7A shows a serpentine shape and moving elements subassemblyconstructed and operative in accordance with a preferred embodiment ofthe present invention. A top static view of the thin foil shows themoving element in this embodiment is typically constructed by etching aprecise round serpentine shape that allows the center of the shape 701freedom of movement restrained by the flexures of the shapes 703 whichhave been etched out of the material, thereby to form interspersingcavities 702. A cross sectional view reveals that the foil typically haspolar aligned layers of magnets, affixed to both the top 704 and thebottom 705 of the tin foil moving element layer. As an alternative tothis embodiment, a layer of magnets may be affixed only to one side ofthe thin foil.

FIG. 7B is an illustrative view of a single element in motion, showingthe upward freedom of movement of certain embodiments where themagnetized center 706 of a single serpentine shape is free to extendupward while being guided and restrained by the serpentine etchedflexures 707. Not shown in the illustration is the opposite (downward)movement of the serpentine shape as it travels in the oppositedirection, and by doing so the flexures extend downward.

In certain embodiments the top of each shape center 708 and the bottomof each layer 709 are affixed magnetized layers that have been alignedin the same magnetic polarity.

FIG. 8A shows a block diagram of the speaker system in accordance with apreferred embodiment of the present invention. In certain embodimentsthe digital input signal (common protocols are I2S, I2C or SPDIF) 801enters into a logic processor 802 which in turn translates the signal todefine the latching mechanism of each grouping of moving elements. Groupaddressing is typically separated into two primary groups, one forlatching the moving elements at the top, and one for latching the movingelements at the bottom of their strokes. Each group is typically thenfurther separated into logical addressing groups typically starting witha group of at least one moving element, followed by another group thatdoubles the moving elements of the previous group, followed by a anothergroup which again doubles the number of elements of the previous, and soon, until all moving elements of the entire array have been grouped. TheNth group comprises 2^(N−1) moving elements.

In the embodiment depicted in the block diagram of FIG. 8A, the topgroup of one element group 803, a two element group 804 and then a fourelement group 805 are shown and so on, until the total numbers of movingelements in the transducer array assembly have been addressed to receivea control signal from the processor 802.

The same grouping pattern is typically replicated for the bottomlatching mechanisms where a one element group 807 may be followed by atwo element group 808 and then a four element group 809 and so on, untilthe total numbers of moving elements in the transducer array assemblyhave been addressed to receive a control signal from the processor 802.

The processor 802 may also control an alternating current flow to thecoil that surrounds the entire transducer array 812, thus creating andcontrolling the magnetic field across the entire array. In certainembodiments a power amplifier 811 may be used to boost current to thecoil.

FIG. 8B illustrates a flow diagram of the speaker system. In certainembodiments where the sampling rate of the digital input signal 813might be different from the device natural sampling rate, the resamplingmodule 814 may re-sample the signal, so that it matches the device'ssampling-rate, Otherwise, the resampling module 814 passes the signalthrough as unmodified.

The scaling module 815 typically adds a bias level to the signal andscales it, assuming the incoming signal 813 resolution is M bits persample, and the sample values X range between −2^((M−1)) and2^((M−1))−1.

It is also assumed that in certain embodiments the speaker array has Nelement groups (numbered 1 . . . N), as described in FIG. 8A.

K is defined to be: K=N−M

Typically, if the input resolution is higher than the number of groupsin the speaker (M>N), K is negative and the input signal is scaled down.If the input resolution is lower than the number of groups in thespeaker (M<N), K is positive and the input signal is scaled up. If theyare equal, the input signal is not scaled, only biased. The output Y ofthe scaling module 815 may be: Y=2^(K)[X+2^(M−1)]. The output Y isrounded to the nearest integer. The value of Y now ranges between 0 and2N−1.

The bits comprising the binary value of Y are inspected. Each bitcontrols a different group of moving elements. The least significant bit(bit1) controls the smallest group (group 1). The next bit (bit2)controls a group twice as big (group 2). The next bit (bit3) controls agroup twice as big as group 2 etc. The most significant bit (bitN)controls the largest group (group N). The states of all the bitscomprising Y are typically inspected simultaneously by blocks 816, 823,. . . 824.

The bits are handled in a similar manner. Following is a preferredalgorithm for inspecting bit1:

Block 816 checks bit1 (least significant bit) of Y. If it is high, it iscompared to its previous state 817. If bit1 was high previously, thereis no need to change the position of the moving elements in group 1. Ifit was low before this, the processor waits for the magnetic field topoint upwards, as indicated by reference numeral 818 and then, asindicated by reference numeral 819, the processor typically releases thebottom latching mechanism 131, while engaging the top latching mechanismT1, allowing the moving elements in group 1 to move from the bottom tothe top of the device.

If block 816 determines that bit1 of Y is low, it is compared to itsprevious state 820. If bit1 was low previously, there is no need tochange the position of the moving elements in group 1. If its previousstate was high, the processor waits for the magnetic field to pointdownwards, as indicated by reference numeral 821 and then, as indicatedby reference numeral 822, the processor releases the top latchingmechanism T1 while engaging the top latching mechanism 131, allowing themoving elements in group 1 to move from the top to the bottom of thedevice.

FIG. 9A shows typical relationships between the different major forcesapplied to moving elements. The different forces being applied to themoving elements typically work in harmony to counterbalance each otherin order to achieve the desired function. Forces toward the center areshown as negative forces, while forces driving the element further awayfrom the center (either toward the up or down latching mechanisms) areshown as positive forces.

In the present embodiment the moving element is influenced by 3 majorforces:

a. Magnetic force, created by the interaction of the magnetic field andthe hard magnet. The direction of this force depends on the polarity ofthe moving element magnet, the direction of the magnetic field and themagnetic field gradient.

b. Electrostatic force, typically created by applying a certain chargeto the electrode and an opposite charge to the moving element. Thedirection of this force is such as to attract the moving element to theelectrode (defined as positive in this figure). This force increasessignificantly when the distance between the moving element and theelectrode becomes very small, and/or where this gap comprises materialwith a high dielectric constant.

c. Retracting force created by the flexures, (which act as springs). Thedirection of this force is always towards the center of the device(defined as negative in this figure). This force is relatively smallsince the flexures are compliant, and is linear in nature.

The relationship between the forces shows that typically, as the movingelement increasingly nears the end of its stroke, the electrostaticforce (generated by the latching mechanism) increases, ultimatelyachieving sufficient force to attract and latch the moving element. Whenthe latch is released, the retracting and magnetic forces are typicallyable to pull the moving element away from the latch toward the center,thereby inducing travel of the moving element. As the moving elementtravels to the center, typically, the retracting force of the flexurediminishes and ultimately is overcome, and is then controlled by theelectromagnetic force and the kinetic energy of the moving element.

FIG. 10A shows a sectional view of the grouping pattern applied incertain embodiments to the moving element (“pistons”) for purposes ofdigital addressing, as described previously in FIG. 8. In thisembodiment there is a group of one element in the center 1001 followedby a two element group 1002, followed by a four element group 1003,followed by a eight element group 1004, followed by a 16 element group1005, and so on.

As shown in this embodiment, to the extent possible each increasinggroup has been arranged to extend around the previous group, howeverthis geometrical configuration can be altered in order to accomplishdifferent audio and/or constructive objectives. For example moving the“epicenter” to the outer circumference of the transducer array enableseasier wire routing between each group and the processor 802 (refer toFIGS. 8A-8B).

FIG. 11A shows a preferred timing and control chart. The time chartdescribes preferred logic and algorithms for generating a specific soundwaveform. In the scope of this description, the timeline is divided intoslots, numbered I1, I2 and so on. This simple example shows a devicethat uses 7 moving elements divided into 3 groups. The first groupcomprises one moving element “P1” and is controlled by the top latchingmechanism “T1” and the bottom latching mechanism “B1”. The second groupcomprises two moving elements “P2” and “P3” which are synchronized andmove together. This group is controlled by the top latching mechanism“T2” and the bottom latching mechanism “B2”. The second group comprisesfour moving elements “P4”, “P5”, “P6” and “P7”, which are synchronizedand move together. This group is controlled by the top latchingmechanism “T3” and the bottom latching mechanism “B3”.

The “clock” chart at the top of the figure represents the system clock.This clock is typically generated outside the device and is transferredto the processor 802 (refer to FIG. 8) alongside the sound signal. In atypical embodiment, the sampling rate of the device is 44100 Hz. In sucha case, the duration of each clock interval is 22 μsec and the clockchanges its state every 11 μsec.

The “signal” shown in this example is the analog waveform that thedevice is generating. The “value” chart shows the digital sample valueof the signal at each clock interval. The “magnetic” chart shows thedirection (polarity) of the magnetic field generated by the coil. Thepolarity changes synchronously with the system clock.

This figure shows the state of each moving element using the followingdisplay convention: An element (“P1” . . . “P7”) that is latched at thetop 1101 is colored in black. An element that is latched at the bottom1102 is colored in white and an element that is moving 1103 is hatched.

The digital sample value dictates how many elements may be latched tothe top and how many to the bottom of the array. In this example,digital sample values of −3, −2, −1, 0, 1, 2, 3, and 4 are possible.Each value is represented by 0, 1, 2, 3, 4, 5, 6 and 7 elements,respectively, latched to the top.

In time slice I1 the digital sample value is 0. This requires 3 elementslatched to the top and 4 to the bottom. The magnetic field polarity isup. The top latching mechanisms T1 and T2 are engaged and so is thebottom latching mechanism B3. At the same time, the bottom latchingmechanisms B1 and B2 are disengaged and so is the top latching mechanismT3. Moving elements P1, P2 and P3 are latched to the top while P4, P5,P6 and P7 are latched to the bottom.

In time slice 13, the digital sample value changes to 1. This requires 4elements latched to the top and 3 to the bottom. The magnetic fieldpolarization is up. The bottom latch 133 is disengaged, releasingelements P4, P5, P6 and P7 to move freely. At the same time, the toplatching mechanism T3 is engaged. The elements move upwards under theinfluence of the magnetic field and are latched by the currently engagedT3.

At this point, all 7 moving elements are latched to the top. In the nextslice 114, the moving elements P1, P2 and P3 would be latched to thebottom, to ensure the device is in the desired state (4 elements at thetop and 3 at the bottom). In slice 14, the polarity of the magneticfield changes and is directed downwards. The top latching mechanisms T1and T2 disengage and release the moving elements P1, P2 and P3. At thesame time, the bottom latching mechanisms B1 and B2 are engaged and theapproaching moving elements P1, P2 and P3 are latched to the bottomposition. The moving elements P4, P5, P6 and P7 are held in place by thetop latching mechanism T3 and are therefore restrained from movingdownwards along with the other moving elements. The state of the deviceat this point is: P1, P2 and P3 are latched to the bottom and P4, P5, P6and P7 are latched to the top. In time slices 15 to 14, the latchingmechanisms are engaged and disengaged to allow the moving elements tomove and change their state according to the digital sample values.

FIG. 12A shows preferred magnetic properties of moving elements foraddressing an alternative embodiment. A static top view of the movingelement foil shows one possible alternative embodiment to the movingelements. In this embodiment two distinct group segments of the movingelements 1201 and 1202 have been created, enabling a single transducerarray to process and generate a louder signal, or alternatively twoseparate signals (such as the left and right audio signal of stereo).The cross section view shows that in order to accomplish the two groupsof this embodiment (discernible by the separated line 1203), eachdistinct group segment typically has opposite magnetic polarity.

In one section group 1201 the layer of magnets affixed to the movingelement of the thin foil has been polarized so that North (N) is on thetop side of the foil 1204 and South (S) is on the bottom side 1205;while in the second section group 1202 the layer of magnets of the thinfoil moving element have been polarized so that South (S) is on the topside of the foil 1206 and North (N) is on the bottom side 1207.

FIG. 13 shows grouping of electrodes in an alternative embodiment.Similar to FIG. 10A, FIG. 13 depicts an alternative addressing schemefor the alternative embodiment that is described in FIG. 12A. In thiscase the grouping pattern applied to the moving element for purposes ofdigital addressing is divided into two primary group segments, half thetransducer array in one primary segment group, and the other half inanother primary segment group, as described in FIG. 12A.

In this embodiment there are two equal groups each with an equal numberof moving elements beginning with two groups 1301 and 1302 of one movingelement each followed by two groups 1303 and 1304 with two elements ineach group followed by two groupings 1305 and 1306 of four elements ineach group, followed by two grouping 1307 and 1308 of eight elements ineach group, followed by two groupings 1309 and 1310 of sixteen elementsin each group and so on, until all moving elements of the transducerarray have been grouped and addressed.

As shown in the current embodiment, to the extent possible, eachincreasing group has been arranged to extend around the previous group,however this geometrical configuration can be altered in order toaccomplish different audio and/or constructive objectives, for examplemoving the “epicenters” to the primary groups to opposite sides of theouter circumference of the transducer array enables easier wire routingbetween each group and the processor 1402 (refer to FIG. 14). It alsoenables the device to operate in two modes: monophonic, where bothgroups are used to generate one waveform at twice the amplitude, andstereophonic, where each group generates a separate sound wave, as toallow reconstruction of a stereophonic signal.

FIG. 14 shows a block diagram of the speaker system in an alternativeaddressing embodiment. FIG. 14 describes addressing of the alternativeembodiment shown in FIGS. 12 and 13. The digital input signal (I2S, I2Cor SPDIF protocols) 1401 enters a logic processor 1402 which in turntranslates the signal to define the latching mechanism of each the twoprimary grouping of moving elements. Each addressing group is separatedinto two primary groups, one for top and one for bottom latchingmechanisms. Each group is then further separated into logical addressinggroups starting with a group of one moving element, followed by anothergroup that doubles the moving elements of the previous group, followedby a another group of double the number of elements of the previousgroup, and so on, until all moving elements of the entire array havebeen grouped.

In the embodiment depicted in the block diagram of FIG. 14, the topstroke of one primary segments of moving elements begins with a oneelement group 1403, and then a two element group 1404, and then a fourelement group 1405, and so on, until the total numbers of movingelements in the transducer array assembly have been addressed to receivea control signal from the processor 1402.

The same grouping pattern is replicated for the down stroke where agroup of one element 1407 is followed by a two element group 1408, andthen a four element group 1409, and so on, until the total numbers ofmoving elements in the transducer array assembly have been addressed toreceive a control signal from the processor 1402.

This same pattern is replicated for the second primary segment of movingelements with the top stroke group starting with a one element group1413, and then a two element group 1414, and then a four element group1415, and so on, until the total numbers of moving elements in thetransducer array assembly have been addressed to receive a controlsignal from the processor 1402.

This is replicated for the down stroke of the second segment beginningwith a group of one element 1417, followed by a two element group 1418,and then a four element group 1419, and so on, until the total numbersof moving elements in the transducer array assembly have been addressedto receive a control signal from the processor 1402.

The processor 1402 will also control an alternating current flow to thecoil that typically surrounds the entire transducer array, includingboth primary segments 1412, thus creating and controlling the magneticfield across the entire array. In certain embodiments a power amplifier1411 may be used to boost current to the coil.

FIG. 15A shows a timing and control chart for an alternative embodiment.A time chart, describing the logic and algorithms, may be used togenerate a specific sound waveform in the alternative embodimentdescribed in FIGS. 12 through 14. The display conventions are similar tothose used in FIG. 11A, and the same signal is reproduced.

The timeline is divided into slots, numbered I1, I2 and so on. Thissimple example shows a device that uses 14 moving elements divided intotwo major groups (L and R), each divided into 3 minor groups 1, 2 and 3.

The digital sample value dictates how many elements may be latched tothe top and how many to the bottom of the array. In this example,digital sample values of −3, 2, −1, 0, 1, 2, 3, and 4 are possible. Eachvalue is represented by 0, 2, 4, 6, 8, 10, 12 and 14 elements,respectively, latched to the top.

On time slice I3, the digital sample value changes from 0 to 1. Thisrequires 8 elements latched to the top and 6 to the bottom. The magneticfield polarization is up. The top latches RT1 and RT2 as well as thebottom latch LB3 are disengaged, releasing elements RP1, RP2, RP3, LP4,LP5, LP6 and LP7 to move freely. The magnetic polarity of LP4, LP5, LP6and LP7 creates an upwards force, driving these elements upwards. Themagnetic polarity of RP1, RP2 and RP3 is opposite and the driving forceis downwards. At the same time, the latching mechanisms opposite to theelement movement are engaged to grab the approaching moving elements andlatch them in place.

On slice I4, the polarity of the magnetic field changes and is directeddownwards. The top latches LT1 and LT2 as well as the bottom latch RB3are disengaged, releasing elements LP1, LP2, LP3, RP4, RP5, RP6 and RP7to move freely. The magnetic polarity of RP4, RP5, RP6 and RP7 createsan upwards force, driving these elements upwards. The magnetic polarityof LP1, LP2 and LP3 is opposite and the driving force is downwards. Atthe same time, the latching mechanisms opposite to the element movementare engaged to grab the approaching moving elements and latch them inplace.

On time slices I5 to I14, the latching mechanisms are engaged anddisengaged to allow the moving elements to move and change their stateaccording to the digital sample values.

FIG. 15C illustrates production of three different pitches (22 KHz, 11KHz and 4.4 KHz) of sound graphs II-IV respectively. Graph I shows thesystem clock which, in the illustrated example is 44 KHz. In theillustrated embodiment, the speaker used to generate these pitches has2047 moving elements. When the 22 KHz sound (half of the clock) isgenerated, all 2047 elements change position (from top to bottom or viceversa) at each clock. When the 11 KHz (quarter of the clock) sound isgenerated, half of the 2047 moving elements change position at eachclock. For example, if in the first clock all 2047 moving elements arein their top position, in the second clock, 1023 of these are lowered,in the third clock the remaining 1024 elements are lowered, in thefourth clock 1023 are raised, in the fifth clock the remaining 1024elements are raised, and so forth. When the 4.4 KHz ( 1/10 of the clock)sound is generated, the numbers of elements which are in their topposition at each clock (1340, 1852, . . . ) are shown on top of Graph IVwhereas the numbers of elements which are in their bottom position ateach clock (707, 195, . . . ) are shown on the bottom of Graph IV.

FIG. 16A shows a small section of the moving elements subassembly.

FIGS. 16A and 16B provide illustrated views of the moving elements indifferent embodiments.

The embodiment shown in FIG. 16A is of moving elements (“Pistons”)constructed from a thin foil material 1601 with a precise roundserpentine shape etched into the material which enables the center ofthe shape 1602 freedom of movement that is restrained by the flexures ofthe shape.

FIG. 16B shows a small section of a different embodiment of the movingelements subassembly, using a flexible substrate. This embodiment is ofmoving elements (“pistons”) constructed from a material with sufficientelasticity, such as rubber polyethylene material 1603, which either hasmagnetic material deposits in specific shapes and dimensions on the topand bottom of the material surface, or the material is affixed to amagnetized disk of particular dimensions 1604, enabling freedom ofmovement that is restrained by the material itself.

FIG. 2C shows a small section of a different embodiment of the movingelements subassembly, using free-floating components. This embodiment isof free floating moving elements (“pistons”) constructed from magnetizedmaterial with polar opposites at each end. In this particular embodimentNorth is on top and South on the bottom.

FIG. 3B illustrates a top view of a complete transducer array structurein certain embodiments, based on a honeycomb design, which enables afill factor of 48 percent of the surface area. FIG. 17 illustrates a topview of a completed transducer array structure in certain embodiments,based on a square design, which enables a fill factor of 38 percent ofthe surface area.

FIG. 18 shows an exploded view of a small section of an embodiment usingsquare shaped elements. This embodiment shows a transducer arraystructure that utilizes square shape elements intended to increase thefill factor and allow higher sound pressure levels per transducer area.

As in previous embodiments, the same structural elements are used. Acoil surrounds the entire transducer array (not shown). When voltage isapplied, the coil generates an electromagnetic actuation force acrossthe entire array structure.

A top layer construction, typically comprising a dielectric layer withan array of accurately spaced cavities 1802, each having an electrodering, is affixed at the top of each cavity, to create an electrostaticlatching mechanism 1801.

The moving elements (“pistons”) in this embodiment comprises a thin foilof conductive magnetized material cut or etched with many very accurate“serpentine” shapes, that imparts the foils a specific measure offreedom of movement 1803 with a magnetized top 1804 and bottom 1805.Each moving element is guided and restrained by four flexures.

A bottom layer construction, typically comprising a dielectric layerwith an array of accurately spaced cavities 1806, each having anelectrode ring affixed at the bottom of each cavity, creates anelectrostatic latching mechanism 1807.

FIG. 19 shows an apparatus including a plurality (array) of devices. Thestructure shows the use of plurality in certain embodiments of arraytransducers 1902 as to create a device 1901 capable of generating loudersound pressure levels or use beam-forming techniques (which extendbeyond the scope of this invention) to create directional sound waves.

The array may have any desired shape, and the round shapes in thedescription are only for illustrative purposes.

The device constructed and operative in accordance with one embodimentof the present invention and described above with reference to FIGS. 1B,2A-2C, 3A-3C, 4A, 5, 6A, 7A-7B, 8A-8B, 9A, 10A, 11A, 12A, 13, 14, 15A,16A-C, 17-19 is now described both more generally, e.g. with referenceto FIG. 1A, and in further detail. Alternative embodiments are alsodescribed.

Reference is now made to FIG. 1A which is a simplified functional blockdiagram illustration of actuator apparatus for generating a physicaleffect, at least one attribute of which corresponds to at least onecharacteristic of a digital input signal sampled periodically inaccordance with a clock. According to a preferred embodiment of thepresent invention, the apparatus of FIG. 1A comprises at least oneactuator device, each actuating device including an array 10 of movingelements each typically constrained to travel alternately back and forthalong a respective axis in response to an alternating electromagneticforce applied to the array 10 of moving elements. Each moving element isconstructed and operative to be responsive to electromagnetic force.Each moving element may therefore comprise a conductor, may be formed ofa Ferro magnetic material, may comprise a permanent magnet e.g. as shownin FIG. 6C, and may comprise a current-bearing coil.

A latch 20 is operative to selectively latch at least one subset of themoving elements 10 in at least one latching position thereby to preventthe individual moving elements 10 from responding to the electromagneticforce. An electromagnetic field controller 30 is operative to receivethe clock and, accordingly, to control application of theelectromagnetic force by a magnetic field generator, 40, to the array ofmoving elements. A latch controller 50 is operative to receive thedigital input signal and to control the latch accordingly. The latchcontroller 50, in at least one mode of latch control operation, isoperative to set the number of moving elements 10 which oscillate freelyresponsive to the electromagnetic force applied by the magnetic fieldgenerator, e.g. coil 40 to be substantially proportional to theintensity of the sound, coded into the digital input signal it receives.Preferably, when the intensity of sound coded into the digital inputsignal is at a positive local maximum, all moving elements are latchedinto a first extreme position. When the intensity of sound coded intothe digital input signal is at a negative local maximum, all movingelements are latched into a second, opposing, extreme position.

Preferably, a physical effect, e.g. sound, resembling the input signalis achieved by matching the number of moving elements in an extremeposition e.g. a top position as described herein, to the digital samplevalue, typically after resampling and scaling as described in detailbelow. For example, if the digital sample value is currently 10, 10moving elements termed herein ME1, . . . ME10 may be in their toppositions. If the digital sample value then changes to 13, threeadditional moving elements termed herein ME11, ME12 and ME13 may beraised to their top position to reflect this. If the next sample valueis still 13, no moving elements need be put into motion to reflect this.If the digital sample value then changes to 16, 3 different movingelements (since ME11, ME12 and ME13 are already in their top positions),termed herein M14, M15 and M16, may be raised to their top positions toreflect this.

In some embodiments, as described in detail below, moving elements areconstructed and operative to be operated collectively in groups, such asa set of groups whose number of moving elements are all sequentialpowers of two, such as 31 moving elements constructed to be operated ingroups having 1, 2, 4, 8, 16 moving elements, respectively, each. Inthis case, and using the above example, when the sample value is, say,10, the two groups including 8 and 2 moving elements respectively areboth, say, up i.e. all moving elements in them are in their toppositions. When the sample value changes to 13, however, it is typicallyimpractical to directly shift 3 moving elements from their bottompositions to their top positions since in this example, due to thebinary grouping, this can only be done by raising the two groupsincluding 1 and 2 moving elements respectively, however, the groupincluding 2 moving elements is already raised. But the number of toppixels may be otherwise matched to the sample value, 13: Since 13=8+4+1,the two groups including 4 and 1 pixels may be raised, and the groupincluding 2 pixels may be lowered, generating a net pressure change of+3, thereby to generate a sound resembling the input signal as desired,typically after re-sampling and scaling.

More generally, moving elements translated toward a first extremeposition such as upward generate pressure in a first direction termedherein positive pressure. Moving elements translated toward the oppositeextreme position such as downward generate pressure in the oppositedirection termed herein negative pressure. A certain amount of positiveor negative pressure may be obtained either by translating theappropriate number of moving elements in the corresponding direction, orby translating n moving elements in the corresponding direction andothers, m in number, in the opposite direction, such that the differencen−m corresponds to e.g. equals the sampled signal value, typically afterre-sampling and scaling.

The moving elements are typically formed of a material which is at leastmoderately electrically conductive such as silicon or silicon coated bya metal such as gold.

If the moving elements comprise permanent magnets, the permanent magnetsare typically magnetized during production such that the magnetic polesare co-linear to the desired axes of motion. A coil that typicallysurrounds the entire transducer array generates the actuation force. Tocontrol each moving element, two latch elements (typically comprisingelectro static latches or “electrodes”) are typically used, e.g. oneabove and one below the moving elements.

According to one embodiment, the actuator is a speaker and the array ofmoving elements 10 is disposed within a fluid medium. The controllers 30and 50 are then operative to define at least one attribute of the soundto correspond to at least one characteristic of the digital inputsignal. The sound has at least one wavelength thereby to define ashortest wavelength present in the sound and each moving element 10typically defines a cross section which is perpendicular to the movingelement's axis and which defines a largest dimension thereof, thelargest dimension of each cross-section typically being small relativeto, e.g. an order of magnitude smaller than, the shortest wavelength.FIG. 1B is an isometric illustration of the array 10 of moving elementsconstructed and operative in accordance with a preferred embodiment ofthe present invention. In this embodiment, each moving element 10comprises a magnet and each is constrained to travel, except when and iflatched, alternately back and forth along a respective axis in responseto an alternating electromagnetic force applied to the array of movingelements 10 by the magnetic field generator 40.

FIGS. 1C-1G are simplified top view illustrations of latch elements 72,73, 74, 76, and 77, any of which may, in combination with similar ordissimilar others form the electrostatic latch 20 in accordance withalternative embodiments of the present invention. At least one of thelatch elements, 72, may have a perforated configuration, as shown inFIG. 1C. In FIG. 1D, a latch element 73 is shown having a notchedconfiguration as to allow concentration of electrostatic charge at thesharp portions of the latch thereby to increase the latching forceapplied to the corresponding moving element. In FIG. 1E, at least onelatch element, 74, has a configuration which includes a central area 75which prevents air from passing so as to retard escape of air, therebyto cushion contact between the moving element 10 and the latchingelement itself. At least one latch element, 76, may have a ringconfiguration, as shown in FIG. 1F and, by way of example, in FIG. 1B.Latch element 77 of FIG. 1G is still another alternative embodimentwhich is similar to latch element 74 of FIG. 1E except that at least oneradial groove 78 is provided so as to eliminate induced current in thelatch.

FIG. 2A shows the array of FIG. 1B in a first, bottom extreme positionresponsive to an electromagnetic force applied, by coil or othermagnetic field generator 40 of FIG. 1A, downward. FIG. 2B shows thearray of FIG. 1B in a second, top extreme position responsive to anelectromagnetic force applied, by coil or other magnetic field generator40 of FIG. 1A, upward. FIG. 2C is similar to FIG. 2B except that one ofthe individual moving magnets, 204, is not responding to the upwardforce applied by magnetic field generator 40 because that individualmagnet is latched into its top extreme position by a correspondingelectric charge disposed above the individual moving element andfunctioning as a top latch. It is appreciated that in the embodiment ofFIGS. 1A-2C, the latch 20 comprises an electrostatic latch, however thisneed not be the case.

Typically, the apparatus of FIGS. 2A-2C comprises a pair of latchelements 205 and 207 for each moving element, termed herein “top” and“bottom” latch elements for simplicity although one need not be abovethe other, the latch elements including one or more electrodes and aspace maintainer 220 separating the electrodes. In embodiments in whichthe latch 20 comprises an electrostatic latch, the space maintainer 220may be formed of an insulating material.

Each pair of latching elements is operative to selectively latch itsindividual moving element 10 in a selectable one of two latchingpositions, termed herein the first and second latching positions or, forsimplicity the “top” and “bottom” latching positions, thereby to preventthe individual moving elements from responding to the electromagneticforce. If the axis along which each moving element 10 moves is regardedas comprising a first half-axis and a second co-linear half-axis, thefirst latching position is typically disposed within the first half-axisand the second latching position is typically disposed within the secondhalf-axis as shown e.g. in FIGS. 2A-2C.

FIGS. 3A-3C are respective top, cross-sectional and isometric views of askewed array of moving elements 10 each constrained to travelalternately back and forth along a respective axis in response to analternating electromagnetic force applied to the array of movingelements 10 e.g. by a coil 40 wrapped around the array as shown. FIG. 4Ais an exploded view of a layered actuator device including an array ofmoving elements 403 each constrained to travel alternately back andforth along a respective axis in response to an alternatingelectromagnetic force applied to the array of moving elements 403 by acoil 401, and a latch, formed as at least one layer, operative toselectively latch at least one subset of the moving elements 403 in atleast one latching position thereby to prevent the individual movingelements 403 from responding to the electromagnetic force. Typically,the electromagnetic force is generated using a coil 401 that surroundsthe array 403 as shown.

The latch typically comprises a pair of layers: a top latch layer 402and bottom latch layer 404 which, when charged, and when the movingelements are in an appropriate electromagnetic field as describedherein, latch the moving elements into top and bottom extreme positionsrespectively. Each of the latch layers 402 and 404 typically comprisesan electrode layer and spacer layer as shown in detail in FIGS. 5-6A.The spacer layers 402 and 404 may generally be formed from any suitabledielectric material. Optionally, ferrite or ferro-magnetic particles maybe added to the dielectric material to decrease undesirable interactionbetween the magnets in the magnet layer.

In FIGS. 5-6A, both flexures and annular magnets or conductors orferromagnets are provided, however it is appreciated that this is notintended to be limiting. Alternatively, for example, other shapedmagnets may be provided, or the annular elements may be replaced bycoils, and free-floating moving elements may be provided withoutflexures, or the moving elements may have a peripheral elastic orflexible portion or be associated with a peripheral elastic or flexiblemember, all as shown and described in detail herein.

FIG. 4B is a simplified flowchart illustration of a preferred actuationmethod operative in accordance with a preferred embodiment of thepresent invention. In FIG. 4B, a physical effect is generated, at leastone attribute of which corresponds to at least one characteristic of adigital input signal sampled periodically in accordance with a systemclock signal. As shown, the method typically comprises (step 450)providing at least one array of moving elements 10 each constrained totravel alternately back and forth along an axis 15 (FIG. 1B) in responseto an alternating electromagnetic force applied to the array of movingelements 10 e.g. by magnetic field generator 40. In step 460, at leastone subset of the moving elements 10 is selectively latched in at leastone latching position by a latch 20 thereby to prevent the individualmoving elements 10 from responding to the electromagnetic force appliedby magnetic field generator 40. In step 470, the system clock signal isreceived and, accordingly, application of the electromagnetic force tothe array of moving elements is controlled. In step 480, the digitalinput signal is received, and the latching step 460 is controlledaccordingly. Typically, as described above, the latch 20 comprises apair of layers, each layer comprising an array of electrostatic latchelements and at least one space maintainer layer separates theelectrostatic latch layers and is formed of an insulating material.Typically, the latch and at least one space maintainer are manufacturedusing PCB production technology (FIG. 48, step 450). The array of movingelements typically comprises a magnetic layer 403 sandwiched between apair of electrode layers spaced from the magnetic layer by a pair ofdielectric spacer layers. Typically, at least one of the layers ismanufactured using wafer bonding technology, layer laminatingtechnology, and/or PCB production technology and/or combination of thesetechnologies (FIG. 4B, step 455).

FIG. 5 is an isometric static view of the actuator device of FIG. 4Aconstructed and operative in accordance with a preferred embodiment ofthe present invention in which the array of moving elements 10 is formedof thin foil, each moving element being constrained by integrally formedflexures 606 surrounding it. The flexures typically include foilportions 703 interspersed with cut-out portions 702. FIG. 6A is anexploded view of a portion of the actuator device of FIG. 5.

According to a preferred embodiment of the present invention, 3 flexuresare provided since at least three flexures are required to define aplane. In the case of the moving elements shown and described herein,the plane defined by the flexures is typically a plane perpendicular tothe desired axes of motion of the moving elements or any plane suitablyselected to constrain the moving elements to travel along the desiredaxes.

Generally, it is desired to minimize the area of the flexures so as toexploit the available area of the device for the moving elementsthemselves since the process of actuation is performed by the movingelements such that, from the point of view of the functionality of thedevice, the area of the flexures is overhead. For example, if theactuator is a speaker, the moving elements push air thereby to createsound whereas the flexures and the gaps defining them do not. Therefore,it is generally desirable that the total length of the flexures besimilar to the perimeter of the moving elements (e.g. as opposed tobeing double the perimeter of the moving elements). Therefore, it may bedesired to treat the total length of the flexures as given andconsequently, the more flexures provided, the shorter each flexure whichtranslates into higher stress under the same translation i.e. to achievethe same amplitude of motion of the moving elements.

As a result, it is believed to be preferable to provide only threeflexures i.e. no more than the minimum number of flexures required tosecurely hold the moving element, e.g. to define a plane normal to theaxis of motion of the moving elements.

FIGS. 6B and 6C are isometric and exploded view illustrations,respectively, of an assembly of moving elements, latches and spacerelements constructed and operative in accordance with a preferred, lowair leakage, embodiment of the present invention. Air leakage refers toair passing from the space above the moving element to the space belowthe moving element or vice versa.

FIG. 6D is a cross-sectional view of the apparatus of FIGS. 6B-6Cshowing three moving elements 10 in top extreme, bottom extreme andintermediate positions 610, 620 and 630 respectively. FIG. 6E is alegend for FIG. 6D. Typically, in the embodiment of FIGS. 6B-6E, atleast one of the moving elements is configured to prevent leakage of airthrough the at least one flexure. As shown, at least one spacemaintainer 640 is disposed between the array of moving elements 10 andthe latching mechanism 20, the space maintainer defining a cylinder 660having a cross section, and wherein at least one of the moving elements10 comprises an elongate element 670 whose cross-section is small enoughto avoid the flexures and a head element 680 mounted thereupon whosecross-section is similar to the cross-section of the cylinder 660. It isappreciated that for simplicity, only a portion of flexures 606 areshown.

FIG. 7A is a static partial top view illustration of the moving elementlayer of FIGS. 5-6C. FIG. 7B is a cross-sectional view of the movingelement layer of FIGS. 5-6 taken along the A-A axis shown in FIG. 7A.FIG. 7C is a perspective view of the moving element layer of FIGS. 5-7Bwherein an individual moving element is shown moving upward toward itstop extreme position such that its flexures bend and extend upward outof the plane of the thin foil. As shown, in FIGS. 7A-7C, at least one ofthe moving elements 10 of FIG. 1A has a cross section defining aperiphery 706 and is restrained by at least one flexure attached to theperiphery. Typically, at least one moving element 10 and its restrainingtypically serpentine flexures are formed from a single sheet ofmaterial. Alternatively, as shown in FIG. 16B, at least one flexure 1605may be formed of an elastic material. It is appreciated that theflexure-based embodiment is only one possible embodiment of the presentinvention. In contrast, as shown e.g. in FIG. 1B, each moving elementmay simply comprise a free floating element.

FIG. 7D is a perspective view of a moving element layer constructed andoperative in accordance with an alternative embodiment of the presentinvention. FIG. 7E is a side view illustration of the flexure-restrainedcentral portion 705 of an individual moving element. In the embodimentof FIGS. 7D-7E, the moving elements 10 of FIG. 1A comprise typicallyannular permanent magnets 710 rather than the disc-shaped permanentmagnets 502 of the embodiments of FIGS. 5-7C. Typically, each movingelement 10 has first and second opposing typically circular surfaces 711and 712 facing first and second endpoints 713 and 714 of the movingelement's axis 715 of motion respectively and at least one permanentmagnet 710 is disposed on at least one of the first and second circularsurfaces 711 and 712. If two permanent magnets 710 are provided, thenthe two are aligned such that the same pole points in the same directionas shown in FIG. 7E.

FIG. 8A is a control diagram illustrating control of latch 20 by latchcontroller 50 of FIG. 1A, and of the typically coil-inducedelectromagnetic force, by controller 30 of FIG. 1A, for a particularexample in which the moving elements 10 are arranged in groups G1, G2, .. . GN that can each, selectably, be actuated collectively, wherein eachlatch in the latching layer is typically associated with a permanentmagnet, and wherein the poles of all of the permanent magnets in thelatching layer are all identically disposed. The latch typicallycomprises, for each group or each moving element in each group, a toplatch and a bottom latch. The top and bottom latches for group Gk (k=1,. . . , N) are termed Tk and Bk respectively. In FIG. 8A the twocontrollers are both implemented in processor 802.

FIG. 8B is a flowchart illustrating a preferred method whereby latchingcontroller 50 of FIG. 1A may process an incoming input signal 801 andcontrol latches 20 of moving elements 10 accordingly, in groups. Theabbreviation “EM” indicates electromagnetic force applied upward ordownward, depending on the direction of the associated arrow, to arelevant group of moving elements. In the embodiment illustrated in FIG.8B, if at time t, the LSB of the re-scaled PCM signal is 1 (step 816),this indicates that the speaker elements in group G1 may be in theselected end-position. If (step 817) group G1 is already in the selectedend-position, no further action is required, however if the group G1 isnot yet in the selected end-position, the latching controller 50 waits(step 818) for the electromagnetic field to be upward and then (step819) releases the bottom latches in set B1 and engages the top latchesin set T1. This is also the case, mutatis mutandis, for all other groupsG2, . . . GN.

In FIG. 8B, the notation Tk or Bk followed by an upward pointing ordownward pointing arrow indicates latching or releasing (upward ordownward arrow respectively) of the top or bottom (T or B respectively)latch of the kith group of moving elements.

FIG. 8C is a simplified functional block diagram illustration of aprocessor, such as the processor 802 of FIG. 8A, which is useful incontrolling substantially any of the actuator devices withelectro-static latch mechanisms shown and described herein. A singleprocessor, in the embodiment of FIG. 8C, implements both electromagneticfield controller 30 and latch controller 50. The electromagnetic fieldcontroller 30 typically receives the system clock 805 which is typicallya square wave and generates a sine wave with the same frequency andphase, providing this to the coil 40 as an actuating signal. The DSP 810may for example comprise a suitably programmed TI 6000 digital signalprocessor commercially available from Texas Instruments. The program forthe DSP 810 may reside in a suitable memory chip 820 such as a flashmemory. The latch controller 50, in at least one mode of latch controloperation, is operative to set the number of moving elements whichoscillate freely responsive to the electromagnetic force applied by thecoil 40 to be substantially proportional to the intensity sound coded inthe digital input signal.

The electromagnetic field controller 30 typically controls analternating current flow to the coil 40 that typically surrounds theentire array of moving elements 10, thus creating and controlling themagnetic field across the entire array. In certain embodiments a poweramplifier 811 may be used to boost current to the coil 40. Theelectromagnetic field controller 30 typically generates an alternatingelectromagnetic force whose alternation is synchronous with the systemclock 805 as described in detail below with reference to FIG. 11A, graphI.

The latch controller 50 is operative to receive the digital input signal801 and to control the latching mechanism 20 accordingly. Typically,each individual moving element 10 performs at most one transition perclock i.e. during one given clock, each moving element may move from itsbottom position to its top position, or move from its top position toits bottom position, or remain at one of either of those two positions.A preferred mode of operation of the latch controller 50 is describedbelow with reference to FIG. 11A. According to a preferred embodiment ofthe present invention, retention of moving elements 10 in theirappropriate end positions is affected by the latching controller 50.

Preferably, the latching controller 50 operates on the moving elementsin groups, termed herein “controlled groups”. All moving elements in anygiven group of moving elements are selectably either latched into theirtop positions, or into their bottom positions, or are unlatched.Preferably, the “controlled groups” form a sequence G1, G2, . . . andthe number of speaker elements in each controlled group Gk is aninteger, such as 2, to the power of (k−1), thereby allowing any desirednumber of speaker elements to be operated upon (latched upward, downwardor not at all) since any given number can be expressed as a sum ofpowers of for example, two or ten or another suitable integer. If thetotal number of speaker elements is selected to be one less than anintegral power (N) of 2 such as 2047, it is possible to partition thetotal population of speaker elements into an integral number ofcontrolled groups namely N. For example, if there are 2047 speakerelements, the number of controlled groups in the sequence G1, G2, . . .is 11.

In this embodiment, since any individual value of the re-scaled PCMsignal can be represented as a sum of integral powers of 2, a suitablenumber of speaker elements can always be placed in the selectedend-position by collectively bringing all members of suitable controlledgroups into that end-position. For example, if at time t the value ofthe re-scaled PCM signal is 100, then since 100=64+32+4, groups G3, G6and G7 together include exactly 100 speaker elements and therefore, atthe time t, all members of these three groups are collectively broughtto the selected end position such as the “up” or “top” position and, atthe same time, all members of all groups other than these three groupsare collectively brought to the un-selected end position such as the“down” or “bottom” position. It is appreciated that each moving elementhas bottom and top latches, each typically generated by selectivelyapplying suitable local electrostatic forces, associated therewith tolatch it into its “down” and “up” positions respectively. The set ofbottom and top latches of the speaker elements in group Gk are termed Bkand Tk latches respectively.

FIG. 8D is a simplified flowchart illustration of a preferred method forinitializing the apparatus of FIGS. 1A-8C. According to the method ofFIG. 8D, the array of moving elements 10 is put into initial motionincluding bringing each moving element 10 in the array of movingelements into at least one latching position. As described herein, bothtop and bottom latching positions are typically provided for each movingelement 10 in which case the step of bringing each moving element in thearray into at least one latching position typically comprises bringing afirst subset of the moving elements in the array into their top latchingpositions and a second subset, comprising all remaining elements in thearray, into their bottom latching positions. The first and secondsubsets are preferably selected such that when the moving elements inthe first and second subsets are in their top and bottom latchingpositions respectively, the total pressure produced by fluid such as airdisplaced by the moving elements 10 in the first subset is equal inmagnitude and opposite in direction to the total pressure produced byfluid such as air displaced by the moving elements in the second subset.

The moving elements 10 typically bear a charge having a predeterminedpolarity and each of the moving elements defines an individual naturalresonance frequency which tends to differ slightly from that of othermoving elements due to production tolerances, thereby to define anatural resonance frequency range, such as 42-46 KHz, for the array ofmoving elements. As described herein, typically, first and secondelectrostatic latching elements are provided which are operative tolatch the moving elements 10 into the top and bottom latching positionsrespectively and the step of putting the array of moving elements intomotion comprises:

Step 850: Charge the first (top or bottom) electrostatic latch of eachmoving element included in the first subset with a polarity opposite tothe pole, on the moving element, facing that latch. The first and secondsubsets may each comprise 50% of the total number of moving elements.

Step 855: Charge the second (bottom or top) electrostatic latch of eachmoving element included in the second subset with a polarity opposite tothe pole, on the moving element, facing that latch.

Step 860: As described above, the moving elements are designed to have acertain natural resonance frequency, f_(r). Design tools may includecomputer aided modeling tools such as finite elements analysis (FEA)software. In step 860, f_(CLK), the frequency of the system clock, whichdetermines the timing of the alternation of the electromagnetic field inwhich the moving elements are disposed, is set to the natural resonancefrequency of the moving element in the array which has the lowestnatural resonance frequency, referred to as f_(min) and typicallydetermined experimentally or by computer-aided modeling.

Steps 865-870: The system clock frequency may then be monotonicallyincreased, from an initial value of f_(min) to subsequent frequencyvalues separated by Δf until the system clock frequency has reached thenatural resonance frequency of the moving element in the array which hasthe highest natural resonance frequency, referred to as f_(max) andtypically determined experimentally or by computer-aided modeling. It isappreciated however that alternatively the system clock frequency mightbe monotonically decreased, from f_(max) to f_(min), or might be variednon-monotonically.

It is appreciated that when a moving element 10 is excited at itsnatural resonance frequency, f_(r), the moving element increases itsamplitude with every cycle, until reaching a certain maximal amplitudetermed hereinafter A_(max). Typically, the duration Δt required for themoving element to reach A_(max) is recorded during set-up and themagnetic force applied during the initialization sequence is selected tobe such that A_(max) is twice as large as the gap the moving elementneeds to travel from its idle state to either the top or bottom latch.

The Q factor or quality factor is a known factor which compares the timeconstant for decay of an oscillating physical system's amplitude to itsoscillation period. Equivalently, it compares the frequency at which asystem oscillates to the rate at which it dissipates its energy. Ahigher Q indicates a lower rate of energy dissipation relative to theoscillation frequency. Preferably, the Q factor of the moving elementsis determined either computationally or experimentally. The Q factor asdetermined describes how far removed the frequency f′_(CLK) needs to befrom f_(r) (two possible values, one below f_(r) and one above f_(r))before the amplitude drops to 50% of A_(max). The difference between thetwo possible values is Δf.

As a result of the above steps, a sequence of electromagnetic forces ofalternating polarities is now applied to the array of moving elements.The time interval between consecutive applications of force of the samepolarity varies over time due to changes induced in the system clock,thereby to define a changing frequency level for the sequence. Thisresults in an increase, at any time t, of the amplitude of oscillationof all moving elements whose individual natural resonance frequency issufficiently similar to the frequency level at time t. The frequencylevel varies sufficiently slowly (i.e. only after a suitable intervalΔt, which may or may not be equal in all iterations) to enable the setS, of all moving elements whose natural resonance frequency is similarto the current frequency level, to be latched before the electromagneticfield alternation frequency level becomes so dissimilar to their naturalresonance frequency as to cease increasing the amplitude of oscillationof the set S of moving elements. The extent of variation of thefrequency level corresponds to the natural resonance frequency range.Typically, at the end of the initiation sequence (step 872), the systemclock f_(CLK) (is set to the predefined system frequency, typicallybeing the average or median natural resonance frequency of the movingelements in the array, i.e. 44 KHz.

One method for determining the range of the natural resonancefrequencies of the moving elements is to examine the array of movingelements using a vibrometer and excite the array at differentfrequencies.

FIG. 8E is a simplified isometric view illustration of an assembledspeaker system constructed and operative in accordance with a preferredembodiment of the present invention. Mounted on a PCB 2100 is the arrayof actuator elements including moving elements 10 (not shown) sandwichedbetween latching elements 20. The array is surrounded by coil 40.Control lines 2110 are shown over which the latch control signalsgenerated by latch controller 50 (not shown) in processor 802 travel tothe latch elements 20. Amplifier 811 amplifies signals provided by themagnetic field generation controller 30 (not shown) in processor 802 tothe coil 40. A connector 2120 connects the apparatus of FIG. 8E to adigital sound source. For simplicity, conventional components such aspower supply components are not shown.

A preferred method of operation for generating a sound using apparatusconstructed and operative in accordance with an embodiment of thepresent invention is now described based on FIG. 8F. The method of FIG.8F is preferably based on the sound's representation in the time domain,typically a PCM (pulse-code modulation) representation.

Resampler 814 of FIG. 8F: Unless the sampling rate of the PCM happens tobe the same as the system clock, the PCM is resampled to bring itssampling rate up to or down to the system clock frequency (top row inFIG. 11A) of the apparatus of FIG. 1A.

Generally, any suitable sampling rate may be employed. Specifically, thesystem of the present invention generates sound waves having at leasttwo different frequencies, one of which is the desired frequency asdetermined by the input signal and the other of which is an artifact.The artifact frequency is the clock frequency i.e. the sampling rate ofthe system. Therefore, preferably, the system sampling rate is selectedto be outside of the human hearing range i.e. at least 20 KHz. Nyquistsampling theory teaches that the system clock must be selected to be atleast double that of the highest frequency the speaker is designed toproduce.

Scaler 815: The PCM word length is typically 8, 16 or 24 bits. 8 bit PCMrepresentations are unsigned, with amplitude values varying over timefrom 0 to 255, and 16 and 24 bit PCM representations are signed, withamplitude values varying over time from −32768 to 32767 and −8388608 to8388607 respectively. The speaker of FIGS. 1-2C typically employs anunsigned PCM signal and therefore, if the PCM signal is signed e.g. ifthe PCM word length is 16 or 24 bits, a suitable bias is added to obtaina corresponding unsigned signal. If the PCM word length is 16 bits, abias of 32768 amplitude units is added to obtain a new range of 0-65535amplitude units. If the PCM word length is 24 bits, a bias of 8388608amplitude units is added to obtain a new range of 0-16777215 amplitudeunits.

The PCM signal is then further re-scaled as necessary such that itsrange, in amplitude units, is equal to the number of speaker elements inthe apparatus of FIGS. 1-2C. For example, if the number of speakerelements is 2047, and the PCM signal is an 8 bit signal, the signal ismultiplied by a factor of 2048/256=8. Or, if the number of speakerelements is 2047, and the PCM signal is a 16 bit signal, the signal ismultiplied by a factor of 2048/65536=1/32.

Sound is then generated to represent the re-scaled PCM signal byactuating a suitable number of speaker elements in accordance with thecurrent value of the re-scaled PCM signal. It is appreciated that thespeaker elements have two possible end-states, termed herein the “down”and “up” end-states respectively, and illustrated schematically in FIGS.2A and 2B respectively. An individual one of these end-states isselected and the number of speaker elements in that end-state at anygiven time matches the current value of the re-scaled PCM signal, theremaining speaker elements at the same time being in the oppositeend-state. For example, if there are 2047 speaker elements, the selectedend-state is “up” and the value of the re-scaled PCM signal at time t is100, the number of speaker elements in the “up” and “down” end states attime t are 100 and 1947 respectively. According to certain embodimentsof the invention, there is no importance to the particular speakerelements selected to be in the “up” state as long as their total numbercorresponds to the current value of the re-scaled PCM signal.

The following loop is then performed M times each time a sample isgenerated by scaler 815. M is the number of actuator elements in theapparatus of FIG. 1A. i is the index of the current loop. V_(t) is usedto designate the current sample value exiting scaler 815 (for which Miterations of the loop are being performed). Generally, the number ofmoving elements to be latched into their top positions, is exactly equalto the value of V_(t) and all remaining moving elements are to belatched into their bottom positions. Therefore, while i is still smallerthan V_(t), the i'th moving element or pixel, termed in FIG. 8F “Pi” islatched to its top position. This is done by checking (FIG. 8F, step840) whether, when moving element i was processed in the previous loop(t−1), it was in its top latching position or in its bottom latchingposition. If the former was the case, nothing needs to be done and themethod jumps to incrementation step 842. If the latter was the case,element i is marked as an element which needs to be latched into its topposition (step 839). To latch all remaining moving elements into theirbottom positions, do the following for all moving elements whose indexexceeds V_(t): check (step 838) which are already in their bottompositions; these moving elements need no further treatment. All othersare marked (step 841) as elements which need to be latched into theirbottom positions. Once all M elements have been marked or not marked asabove, perform the following:

Verify that the magnetic field points upward, or wait for this (step843), and, for the V_(t) or less pixels which are to be raised,discharge the bottom latches and charge the top latches (step 844).Next, wait for the magnetic field to point downward (step 845), and, forthe (M−V_(t)) or less pixels which are to be lowered, discharge the toplatches and charge the bottom latches (step 846). At this point, theflow waits for the next sample to be produced by scaler 815 and thenbegins the M iterations of the loop just described for that sample.

It is appreciated that steps preceding step 843 are preferably executedduring the half clock cycle in which the magnetic field polarity isdownwards. Step 844 is preferably executed at the moment the magneticfield changes its polarity from downwards to upwards. Similarly, step846 is preferably executed at the moment the magnetic field changespolarity again from upwards to downwards. It is also appreciated that inorder for the device to remain synchronized with the digitized inputsignal, steps 814-846 are all preferably executed in less than one clockcycle.

FIG. 9A is a graph summarizing the various forces brought to bear onmoving elements 10 in accordance with a preferred embodiment of thepresent invention.

FIG. 9B is a simplified pictorial illustration of a magnetic fieldgradient inducing layer constructed and operative in accordance with apreferred embodiment of the present invention and comprising at leastone winding conductive element 2600 embedded in a dielectric substrate2605 and typically configured to wind between an array of channels 2610.Typically, there are no channels 2610 along the perimeter of theconductive layer of FIG. 9B so that the gradient induced within channelsadjacent the perimeter is substantially the same as the gradient inducedin channels adjacent the center of the conductive layer.

If the layer of FIG. 9B is separate from the spacer layers describedabove, then the channels in the layer of FIG. 9B are disposed oppositeand as a continuation of the channels in the spacer layers described indetail above. The cross-sectional dimensions, e.g. diameters, ofchannels 2610 may be different than the diameters of the channels in thespacer layer. Alternatively, the layer of FIG. 9B may serve both as aspacer layer and as a magnetic field inducing layer in which case thechannels 2610 of FIG. 9B are exactly the spacer layer channels describedhereinabove. It is appreciated that, for simplicity, the electrodesforming part of the spacer layer are not shown in FIG. 98.

FIGS. 9C and 9D illustrate the magnetic field gradient inductionfunction of the conductive layer of FIG. 9B. In FIG. 9C, the currentflowing through the winding element 2600 is indicated by arrows 2620.The direction of the resulting magnetic field is indicated by X's 2630and encircled dots 2640 in FIG. 9C, indicating locations at which theresulting magnetic field points into and out of the page, respectively.

FIG. 10A is a simplified top cross-sectional illustration of a latchinglayer included in latch 20 of FIG. 1A in accordance with a preferredembodiment of the present invention. The latching layer of FIG. 10A issuitable for latching moving elements partitioned into several groupsG1, G2, . . . whose latches are electrically interconnected as shown soas to allow collective actuation of the latches. This embodiment istypically characterized in that any number of moving elements may beactuated by collectively charging the latches of selected groups fromamong the partitioned groups, each latch in the latching layer typicallybeing associated with a permanent magnet, wherein the poles of all ofthe permanent magnets in the latching layer are all identicallydisposed. Each group Gk may comprise 2 to the power of (k−1) movingelements. The groups of moving elements may spiral out from the centerof the array of moving elements, smallest groups being closest to thecenter as shown.

FIG. 10B is a simplified electronic diagram of an alternative embodimentof the latching layer of FIG. 10A in which each latch is individuallyrather than collectively controlled (i.e. charged) by the latchingcontroller 50 of FIG. 1A. It is appreciated that the latches are shownto be annular, however alternatively they may have any other suitableconfiguration e.g. as described herein. The layer of FIG. 10B comprisesa grid of vertical and horizontal wires defining junctions. A gate suchas a bi-polar field-effect transistor is typically provided at eachjunction. To open an individual gate thereby to charge the correspondinglatch, suitable voltages are provided along the corresponding verticaland horizontal wires.

FIG. 11A is a timing diagram showing a preferred charging control schemewhich may be used by the latch controller 50 in FIG. 1A inuni-directional speaker applications wherein an input signalrepresenting a desired sound is received, and moving elements 10constructed and operative in accordance with a preferred embodiment ofthe present invention are controlled responsively, by appropriatecharging of their respective latches, so as to obtain a sound pattern inwhich the volume in front of the speaker is greater than in other areas,each latch in the latching layer being associated with a permanentmagnet, and the poles of all of the permanent magnets in the latchinglayer all being identically disposed. FIG. 11B is a schematicillustration of an example array of moving elements 10 to which thetiming diagram of FIG. 11A pertains.

A preferred mode of operation of the latch controller 50 is nowdescribed with reference to FIGS. 11A-B. For clarity, the preferred modeof operation is described merely by way of example with reference to aspeaker comprising 7 pixels numbered P1, P2, . . . P7 as shown in FIG.11B. Further according to the example used to explain the preferred modeof operation of latch controller 50, the 7 pixels are actuated in threegroups comprising 1, 2 and 4 pixels respectively. Generally, the latchcontroller 50 uses various decision parameters, as described in detailherein, to determine how to control each individual moving element ineach time interval. Speakers constructed and operative in accordancewith a preferred embodiment of the present invention are typicallyoperative to reproduce a sound which is represented by the analog signalof Graph II and is then digitized and supplied to a speaker of thepresent invention. The values of the digital signal are shown in FIG.11A, graph III.

Graph IV shows the alternation of the electromagnetic force applied tothe moving elements 10 by the coil or other magnetic field generator 40.Graph V is the signal provided by latching controller 50 to the toplatch of an individual moving element, P1 seen in FIG. 11B, forming, onits own, a first group G1 of moving elements consisting only of P1.Graph VI is the signal provided by latching controller 50 to the bottomlatch of P1. The states of P1, due to the operation of the latchesassociated therewith, are shown in Graph VII, in which black indicatesthe top extreme position in which the top latch engages P1, whiteindicates the bottom extreme position in which the bottom latch engagesP1, and hatching indicates intermediate positions.

Graph VIII is the signal provided by latching controller 50 to the toplatch/es of each of or both of, moving elements P2 and P3 seen in FIG.11B, which together form a second group GII of moving elements. Graph IXis the signal provided by latching controller 50 to the bottom latch/esof GII. The states of P2 and P3, due to the operation of the latchesassociated therewith, are shown in Graphs X and XI respectively, inwhich black indicates the top extreme position in which the top latchengages the relevant moving element, white indicates the bottom extremeposition in which the bottom latch engages the relevant moving element,and hatching indicates intermediate positions of the relevant movingelement.

Graph XII is the signal provided by latching controller 50 to the toplatch/es of each of, or all of, moving elements P4-P7 seen in FIG. 11B,which together form a third group GIII of moving elements. Graph XIII isthe signal provided by latching controller 50 to the bottom latch/es ofGIII. The states of P4-P7, due to the operation of the latchesassociated therewith, are shown in Graphs XIV-XVII respectively, inwhich black indicates the top extreme position in which the top latchengages the relevant moving element, white indicates the bottom extremeposition in which the bottom latch engages the relevant moving element,and hatching indicates intermediate positions of the relevant movingelement.

Graph XVIII schematically illustrates the moving elements P1-P7 of FIG.11B in their various positions, as a function of time.

For example, in interval I5, the clock is high (graph I), the digitizedsample value is 2 (graph III), which indicates that 5 elements need tobe in their top positions and 2 elements in their bottom positions asshown in interval I5 of Graph XVIII. Since latch actuation in thisembodiment is collective, this is achieved by selecting groups G1 and G3which together have 5 elements (1+4) to be in their top positionswhereas the two moving elements in G2 will be in their bottom positions.The magnetic field points upward in interval I5 as shown in Graph IV. Ininterval I4, the moving element in G1 was in its bottom position asshown in Graph XVIII and therefore needs to be raised. To do so, controlsignal B1 is lowered (graph VI) and control signal T1 is raised (graphV). As a result, the moving element of G1 assumes its top position asshown in graph VII. In interval I4, the moving elements in G2 arealready in their bottom positions as shown in Graph XVIII and thereforethe top control signal T2 remains low as seen in graph VIII, the bottomcontrol signal B2 remains high as seen in graph IX and consequently, asshown in Graphs X and XI respectively, the two moving elements (P2 andP3) in G2, remain in their bottom extreme positions. As for group G3, ininterval I4, the moving elements in G3 are already in their toppositions as shown in Graph XVIII and therefore the top control signalT3 remains high as seen in graph XII, the bottom control signal B3remains low as seen in graph XIII and consequently, as shown in GraphsXIV-XVII respectively, the four moving elements (P4-P7) in G3, remain intheir top extreme positions.

Preferably, when the input signal in graph II is at a positive localmaximum, all moving elements are in their top position. When the inputsignal is at a negative local maximum, all moving elements are in theirbottom position.

FIG. 11C is a timing diagram showing a preferred control scheme used bythe latch controller 50 in omni-directional speaker applications whereinan input signal representing a desired sound is received, and movingelements constructed and operative in accordance with a preferredembodiment of the present invention are controlled responsively, so asto obtain a sound pattern in which the loudness of the sound in an arealocated at a certain distance in front of the speaker is similar to theloudness in all other areas surrounding the speaker at the same distancefrom the speaker.

As shown, the step of selectively latching comprises latching specificmoving elements at a time determined by the distance of the specificmoving elements from the center of the array (e.g. as indicated by r inthe circular array of FIG. 11B). Typically, when it is desired to latcha particular subset of moving elements, typically corresponding innumber to the intensity of a desired sound, the moving elements arelatched not simultaneously but rather sequentially, wherein movingelements closest to the center are latched first, followed by thosemoving elements disposed, typically in layers, concentrically outwardfrom the center. Typically, the moving elements in each layer areactuated simultaneously. Typically, the temporal distance Δt between themoment at which a particular moving element is latched and between themoment at which the first, central, moving element or elements was orwere latched is r/c where c is the speed of sound.

It is appreciated that the moving elements in graph X of FIG. 11C areshown to comprise flexible peripheral portions, however this is merelyby way of example and is not intended to be limiting.

FIGS. 12A and 12B are respectively simplified top view andcross-sectional view illustrations of the moving element layer inaccordance with a preferred embodiment of the present invention in whichhalf of the permanent magnets are placed north pole upward and halfnorth pole downward. A particular advantage of this embodiment is thatmoving elements can be raised both when the electromagnetic field pointsupward and when it points downward rather than waiting for the field topoint upward before lifting a moving element and waiting for the fieldto point downward before lowering a moving element. Although theillustrated embodiment shows the two subsets separated from one another,this not need be the case. The two subsets may be interleaved with oneanother.

FIG. 13 is a simplified top view illustration similar to FIG. 10A exceptthat half of the permanent magnets in the latching layer are disposednorth pole upward and the remaining half of the permanent magnets in thelatching layer are disposed north pole downward. Whereas in theembodiment of FIG. 10A, there was one group each of size 1, 2, 4, . . .(which may be arranged sequentially around the center as shown in FIG.10A although this need not be the case) in the embodiment of FIG. 13,there are two groups of each size, thereby generating two sequences ofgroups of size 1, 2, 4, . . . . In the illustrated embodiment the groupsin the first sequence are termed G1L, G2L, G3L, and the groups in thefirst sequence are termed G1R, G2R, G3R, . . . . Each of these sequencesis arranged within one semicircle, such as the left and rightsemicircles as shown. The arrangement of the groups within itssemicircle need not be in order of size of the group extendingconcentrically outward as shown and can be any desired arrangement,however, preferably, both groups are arranged mutually symmetricallywithin their individual semicircle. It is appreciated that by usingsuitable coil designs, the same effect can be achieved using permanentmagnets that are all polarized in the same direction while the coilgenerates magnetic fields having a certain polarization across half ofthe moving elements and having an opposite polarization across the otherhalf.

A particular feature of the embodiments of FIGS. 10A and 13 is thatlatch elements corresponding to certain moving elements are electricallyinterconnected thereby to form groups of moving elements which can becollectively latched or released by collectively charging ordischarging, respectively, their electrically interconnected latches.

FIG. 14 is a control diagram illustrating control of the latches and ofthe coil-induced electromagnetic force for a particular example in whichthe moving elements are arranged in groups that can each, selectively,be actuated collectively, similar to FIG. 8A except that half of thepermanent magnets in the latching layer are disposed north pole upwardand the remaining half of the permanent magnets in the latching layerare disposed north pole downward as shown in FIG. 13, whereas in FIG.8A, the poles of all of the permanent magnets in the latching layer areall identically disposed. As shown in FIG. 14, latching signals areprovided to all of groups G1L, G2L, G3L, and G1R, G2R, G3R. The toplatching signals for these groups are indicated as LT1, LT2, LT3, andRT1, RT2, RT3 respectively. The bottom latching signals for these groupsare indicated as LB1, LB2, LB3, and RB1, RB2, RB3.

FIG. 15A is a timing diagram showing a preferred control scheme used bythe latch controller 50 in uni-directional speaker applications, whichis similar to the timing diagram of FIG. 11A except that half of thepermanent magnets in the latching layer are disposed north pole upwardand the remaining half of the permanent magnets in the latching layerare disposed north pole downward as shown in FIG. 13 whereas in FIG. 11Athe poles of all of the permanent magnets in the latching layer are allidentically disposed. FIG. 15B is a schematic illustration of an examplearray of moving elements to which the timing diagram of FIG. 15Apertains.

As described above, a particular advantage of the embodiment of FIGS.13-15A as opposed to the embodiment of FIGS. 8A, 10A and 11A is thatmoving elements can be raised both when the electromagnetic field pointsupward and when it points downward rather than waiting for the field topoint upward before lifting a moving element and waiting for the fieldto point downward before lowering a moving element. It is appreciatedthat no elements move in 50% of the time slots in FIG. 11A which mayintroduce distortion of sound and is relatively inefficient. Incontrast, elements move in 100% of the time slots in FIG. 15A (otherthan slots in which no motion is required since the digital signal valueis unchanged) thereby preventing distortion and enhancing efficiency.

For example, in interval I5, the digitized signal value changes from 1to 2 as shown in graph II of FIGS. 11A and 15A. Consequently, movingelement P1 in FIG. 11A needs to be raised i.e. released from itscurrent, bottom extreme position and latched into its top extremeposition, however whereas in I5, control signal 131 is lowered andcontrol signal T1 is raised, in interval I6 nothing happens. In FIG.15A, in contrast, where moving elements LP1 (and RPI) need to be raised,control signal LB1 is lowered and control signal LT1 is raised ininterval I5, and immediately afterward, in interval I6, the R131 controlsignal is lowered and the RT1 signal is raised, resulting in upwardmotion of RPI without the delay incurred in FIG. 11A.

Generally in the embodiment of FIGS. 13-15A, since half of the magnets(say, the left half) point north up and the remaining (right) half pointnorth down, when it is desired to move elements 10 upward, this canalways be done without delay. If the magnetic field points up, themoving elements in the left half of the array can be moved upward beforethose in the right half, whereas if by chance the magnetic field isfound to be pointing down, the moving elements in the right half of thearray can be moved upward before those in the left half.

FIG. 15C is a graph showing changes in the number of moving elementsdisposed in top and bottom extreme positions at different times and as afunction of the frequency of the input signal received by the latchingcontroller 50 of FIG. 1A.

FIG. 16A is an isometric view illustration of a moving element layerwhich is an alternative to the moving element layer shown in FIGS. 1Aand 2A-2C in which the layer is formed from a thin foil such that eachmoving element comprises a central portion and surrounding portions.

FIG. 16B is an isometric view illustration of still another alternativeto the moving element layer shown in FIGS. 1A and 2A-2C in which theflexure structure at the periphery of each moving element comprises asheet of flexible material e.g. rubber. The central area of each movingelement comprises a magnet which may or may not be mounted on a rigiddisc.

FIG. 16C is an isometric view of a preferred embodiment of the movingelements and surrounding flexures depicted in FIG. 7A-7E or 16A in whichflexures vary in thickness. In FIG. 16C, for simplicity, the componentwhich causes the moving element 1620 to be affected by the magneticfield, which component may preferably comprise a magnet oralternatively, a Ferro-magnet, conductive material or coil, is notshown. As shown, the moving element 1620 comprises serpentine peripheralflexures 1630 having portions of varying thicknesses connecting acentral portion 1640 of the moving element to a sheet 1650interconnecting all or many moving elements. For example, the portionsof varying thicknesses may include thicker portions 1660 and thinnerportions 1670 respectively as shown. For example, if the diameter of thecentral portion 1640 of each moving element is 300 microns and the sheetis silicon, then under certain conditions, portions 1670 may be 50microns thick whereas portions 1660 may be 100 microns thick. Moregenerally, thicknesses are computed as a function of materials toprovide application-specific flexibility and strength levels, e.g. usingFEA (finite element analysis) tools.

FIG. 16D is an isometric illustration of a cost effective alternative tothe apparatus of FIG. 16C in which flexures vary in width. As in FIG.16C, for simplicity, the component which causes the moving element 1720to be affected by the magnetic field, which component may preferablycomprise a magnet or alternatively, a ferro-magnet, conductive materialor coil, is not shown. As shown, the moving element 1720 comprisesserpentine peripheral flexures 1730 having portions of varying widthsconnecting a central portion 1740 of the moving element to a sheet 1750interconnecting all or many moving elements. For example, the portionsof varying widths may include wider portions 1760 and narrower portions1770 respectively as shown. For example, if the diameter of the centralportion 1740 of each moving element is 300 microns and the sheet issilicon, then under certain conditions, portions 1770 may be 20 micronswide whereas portions 1760 may be 60 microns wide. More generally,widths are computed as a function of materials to provideapplication-specific flexibility and strength levels, e.g. using FEA(finite element analysis) tools.

It is appreciated that the embodiments of FIGS. 16C and 16D may besuitably combined, e.g. to provide flexures with varying thicknesses andvarying widths, and/or varied, e.g. to provide flexures whose widthsand/or thicknesses vary either continuously or discontinuously as shown,and either regularly as shown or irregularly.

In the above description, “thickness” is the dimension of the flexure inthe direction of motion of the moving element whereas “width” is thedimension of the flexure in the direction perpendicular to the directionof motion of the moving element.

A particular advantage of the embodiments of FIGS. 16C and 16D is thatin flexures of varying cross-sections, e.g. varying thicknesses orwidths, the stress is not concentrated at the roots 1680 or 1780 of theflexures and is instead distributed over all the thin and/or narrowportions of the flexures. Also, generally, the stress on the flexures asa result of bending thereof is a steep function of the thickness,typically a cubic function thereof, and is also a function of the width,typically a linear function thereof. It is believed to be impractical,at least for certain materials such as silicon and at least for certainapplications employing large displacement of the moving elements, e.g.public address speakers, to select flexure dimensions which areuniformly thin enough or narrow enough to provide sufficiently lowstress so as to prevent breaking, and simultaneously stiff enough toallow natural resonance frequency at a desirable range e.g. 44 KHz. Forthis reason as well, it is believed to be advantageous to use flexuresof varying thicknesses and/or widths e.g. as illustrated in FIGS.16C-16D.

FIG. 17 is a top cross-sectional view illustration of an array ofactuator elements similar to the array of FIG. 3A except that whereas inFIG. 3A, consecutive rows of individual moving elements or latches arerespectively skewed so as to increase the number of actuator elementsthat can be packed into a given area, the rows in FIG. 17 are unskewedand typically comprise a rectangular array in which rows are mutuallyaligned.

FIG. 18 is an exploded view of an alternative embodiment of an array ofactuator elements, including a layer 1810 of moving elements sandwichedbetween a top latching layer 1820 and a bottom latching layer 1830. Theapparatus of FIG. 18 is characterized in that the cross-section of eachactuator element is square rather than round. Each actuator elementcould also have any other cross-sectional shape such as a hexagon ortriangle.

FIG. 19 is an isometric array of actuators supported within a supportframe providing an active area which is the sum of the active areas ofthe individual actuator arrays. In other words, in FIG. 19, instead of asingle one actuating device, a plurality of actuating devices isprovided. The devices need not be identical and can each have differentcharacteristics such as but not limited to different clock frequencies,different actuator element sizes and different displacements. Thedevices may or may not share components such as but not limited to coils40 and/or magnetic field controllers 30 and/or latch controller 50.

The term “active area” refers to the sum of cross-sectional areas of allactuator elements in each array. It is appreciated that generally, therange of sound volume (or, for a general actuator other than a speaker,the gain) which can be produced by a speaker constructed and operativein accordance with a preferred embodiment of the present invention isoften limited by the active area. Furthermore, the resolution of soundvolume which can be produced is proportional to the number of actuatorelements provided, which again is often limited by the active area.Typically, there is a practical limit to the size of each actuator arraye.g. if each actuator array resides on a wafer.

If the speaker is to serve as a headphone, only a relatively small rangeof sound volume need be provided. Home speakers typically require anintermediate sound volume range whereas public address speakerstypically have a large sound volume range, e.g. their maximal volume maybe 120 dB. Speaker applications also differ in the amount of physicalspace available for the speaker. Finally, the resolution of sound volumefor a particular application is determined by the desired sound quality.e.g. cell phones typically do not require high sound quality, howeverspace is limited.

According to certain embodiments of the present invention, layers ofmagnets on the moving elements may be magnetized so as to be polarizedin directions other than the direction of movement of the element toachieve a maximum force along the electromagnetic field gradient alignedwith the desired element moving direction.

Referring again to FIGS. 12A-15B inter alia, it is appreciated that ifthe coil used is of a design that utilizes conductors carrying currenton both sides of the elements, and the magnets are all polarized in thesame direction, then the elements on one side of each conductor wouldmove in opposite directions when current flows in the coil.

A particular feature of a preferred embodiment of the present inventionis that the stroke of motion performed by the moving elements isrelatively long because the field applied thereto is magnetic hencedecays at a rate which is inversely proportional to the distance betweenthe moving elements and the current producing the magnetic field. Incontrast, an electrostatic field decays at a rate which is inverselyproportional to the square of the distance between the moving elementsand the electric charge producing the electrostatic field. As a resultof the long stroke achieved by the moving elements, the velocityachieved thereby is increased hence the loudness that can be achievedincreases because the air pressure generated by the high velocity motionof the moving elements is increased.

It is appreciated that the embodiments specifically illustrated hereinare not intended to be limiting e.g. in the sense that the movingelements need not all be the same size, the groups of moving elements,or individual moving elements if actuated individually, need not operateat the same resonance nor with the same clock, and the moving elementsneed not have the same amplitude of displacement.

The speaker devices shown and described herein are typically operativeto generate a sound whose intensity corresponds to intensity valuescoded into an input digital signal. Any suitable protocol may beemployed to generate the input digital signal such as but not limited toPCM or PWM (SACD) protocols. Alternatively or in addition the device maysupport compressed digital protocols such as ADPCM, MP3, AAC, or AC3 inwhich case a decoder typically coverts the compressed signal into anuncompressed form such as PCM.

Design of digital loudspeakers in accordance with any of the embodimentsshown and described herein may be facilitated by application-specificcomputer modeling and simulations. Loudness computations may beperformed conventionally, e.g. using fluid dynamic finite-elementcomputer modeling and empiric experimentation.

Generally, as more speaker elements (moving elements) are provided, thedynamic range (difference between the loudest and softest volumes thatcan be produced) becomes wider, the distortion (the less the soundresembles the input signal) becomes smaller and the frequency rangebecomes wider. On the other hand, if less speaker elements are provided,the apparatus is smaller and less costly.

Generally, if the moving elements have large diameters, the ratiobetween active and inactive areas (the fill factor) improves, and thereis less stress on the flexures if any, assuming that the vibrationdisplacement remains the same, which translates into longer lifeexpectancy for the equipment. On the other hand, if the moving elementshave small diameters, more elements are provided per unit area, and dueto the lesser mass, less current is required in the coil or otherelectromagnetic force generator, translating into lower powerrequirements.

Generally, if the vibration displacement of the moving elements islarge, more volume is produced by an array of a given size, whereas ifthe same quantity is small, there is less stress on the flexures, ifany, and the power requirements are lower.

Generally, if the sample rate is high, the highest producible frequencyis high and the audible noise is reduced. On the other hand, if thesample rate is low, accelerations, forces, stress on flexures if any andpower requirements are lower.

Three examples of application-specific speakers are now described.

Example 1

It may be desired to manufacture a mobile phone speaker which is verysmall, is low cost, is loud enough to be heard ringing in the next room,but has only modest sound quality. The desired small size and costsuggest a speaker with relatively small area, such as up to 300 mm². Ifa relatively high target maximal loudness such as 90 dB SPL is desired,this suggests large displacement. Acceptable distortion levels (10%) anddynamic range (60 dB) in mobile phone speakers dictate a minimal arraysize of 1000 elements (computed using: M=10^((60/20))). Therefore, asuitable speaker may comprise 1023 moving elements partitioned into 10binary groups, each occupying an area of about 0.3 mm². The cell sizewould therefore be about 550 μm×550 μm.

For practical reasons, the largest moving element that fits this spacemay have a diameter of 450 μm. Reasonable displacement for such a movingelement may be about 100 μm PTP (peak to peak) which enables the targetloudness to be achieved. The sample rate may be low, e.g. 32 KHz, sincemobile phones sound is limited by the cellular channel to 4 KHz.

Example 2

It may be desired to manufacture high fidelity headphones having veryhigh sound quality (highest possible) and very low noise, and which areadditionally small enough to be worn comfortably, and finally,cost-effective to the extent possible.

To achieve high sound quality, wide dynamic range (at least 96 dB), widefrequency range (20 Hz-20 KHz) and very low distortion (<0.1%) may beused. The minimal number of elements may be, given these assumptions,63000. So, for example, the speaker may have 65535 elements divided into16 binary groups. Maximal loudness can be kept low (80 dB) so as toallow displacements of about 30 μm PTP. The smallest moving elementcapable of such displacements is about 150 μm in diameter. Such anelement may occupy a cell of 200 μm×200 μm or 0.04 mm² such that 65535elements fit into an area of 2621 mm² e.g. 52 mm×52 mm. The sample rateis typically at least twice the highest frequency the speaker is meantto produce, or 40 KHz. The closest standard sample rate is 44.1 KHz.

Example 3

It may be desired to manufacture a public address speaker, e.g. for adance club, which is very loud, has a wide frequency range, extends tovery low frequencies, and has low distortion. Therefore, PA speakerstypically have many large moving elements. 600 μm moving elements may beused, which are capable of displacements of 150 μm PTP. Such elementsoccupy cells of 750 μm×750 μm or 0.5625 mm². Due to the low frequencyrequirement, a minimum of 262143 moving elements, partitioned into 18binary groups, may be used. The size of the speaker may be about 40cm×40 cm. This speaker typically reaches maximal loudness levels of 120dB SPL and extends down to 15 Hz.

Reference is now made to FIGS. 20A-20B which is are simplified generallyself-explanatory functional block diagram illustration of preferredsystems for achieving a desired directivity pattern for a desired soundstream using a direct digital speaker such as any of those shown hereinin FIGS. 1A-19 or such as a conventional direct digital speaker whichmay, for example comprise that shown and described in U.S. Pat. No.6,403,995 to David Thomas, assigned to Texas Instruments and issued 11Jun. 2002, or in Diamond Brett M., et al, “Digital sound reconstructionusing array of CMOS-MEMS micro-speakers”, Transducers '03, The 12^(th)International Conference on Solid State Sensors, Actuators andMicrosystems, Boston, June 8-12, 2003.

If the direct digital speaker of FIG. 1A is used to achieve a desireddirectivity pattern for a desired sound stream, then typically, blocks3020, 3030 and 3040 in FIG. 20A comprise blocks 20, 30 and 40 of FIG. 1Arespectively and block 3050 comprises latch controller 50 of FIG. 1A,programmed to implement the per-clock operation of block 3050 e.g. asshown and described herein with reference to FIG. 21.

FIG. 21 is a simplified flowchart illustration of per-clock operation ofthe moving element constraint controller 3050 of FIGS. 20A-20B, inaccordance with certain embodiments of the present invention.

Step 3100 determines how many moving elements should move during thecurrent clock. Typically, and as described in detail above withreference to FIGS. 1-19, the number of moving elements which are to moveduring a given clock is generally proportional to the intensity of theinput signal during that clock, suitably normalized e.g. as describedabove with reference to resampler 814 and scaler 815 of FIG. 8B.

Step 3200 determines which moving elements should move during thecurrent clock, using, in some embodiments, a suitable moving elementselection LUT which is typically loaded into the memory of theconstraint controller 3050 of FIGS. 20A-20B during factory set-up. Eachsuch LUT is typically built for a specific moving element array takinginto account, inter alia, the array size and whether or not the array isskewed. Each directivity pattern which it is desired to achievetypically requires its own LUT.

Step 3300 determines the amount of delay with which to operate each ofthe moving elements of moving element array 3010 or 3012 of FIGS.20A-20B.

Step 3200 is now described in detail. A preferred method for performingstep 3200 is now described. Step 3200 typically employs a LUT (look uptable) which has cells which correspond one-to-one to the pressureproducing elements in the array. For example, if the array comprises arectangle of 100×200 pressure producing elements then the LUT may have100×200 cells. Each cell holds a uniquely appearing integer between 1and the total number of pressure producing elements such as 20000 in theillustrated example. Therefore, the LUT assigns an ordinal number toeach pressure producing element in the array. Associated in memory withthe LUT is a integer parameter P which stores an indication of thenumber of pressure producing elements currently in a first operativeconfiguration from among two operative configurations, characterized inthat transition of the pressure producing elements therebetween producespressure in the medium, such as air, in which the apparatus of theinvention is disposed. In some embodiments, pressure in oppositedirections is obtained when the elements move from the firstconfiguration to the second, as opposed to when the elements move fromthe second configuration to the first. In other embodiments, pressure isobtained as long as the elements are in the first configuration, and nopressure is obtained when the elements are in the second configuration.

Typically, P is initialized during set-up as described below, and isthen assigned a current value in each clock by step 3100. In theimmediately following step 3200 in the same clock, P pressure producingelements are brought to their first operative configuration and N-Ppressure producing elements are brought to their second operativeconfiguration where N is the number of pressure producing elements inthe array. The P elements selected to be in their first operativeconfiguration are those whose ordinal number as determined by the LUT issmaller than P. The N-P elements selected to be in their secondoperative configuration are those whose ordinal number as determined bythe LUT is greater than or equal to P.

One of these configurations, say the first, is typically arbitrarilyconsidered the “positive” configuration whereas the other configuration,say the second, is then considered the “negative” configuration.Alternatively, in some applications there may be a physical reason toselect a specific one of the configurations to be the positiveconfiguration. The pressure generated when a pressure producing elementmoves from the second configuration to this first configuration istermed “positive pressure” whereas the pressure generated when apressure producing element moves from the second configuration to thisfirst configuration is termed “positive pressure”. The pressuregenerated by a single transition from one configuration to the other istermed herein a pressure “pulse”.

During set-up, the parameter P is typically given an initial value equalto half of the number of pressure producing elements in the array suchas 10000 in the present example. The array is then initialized such thateach pressure producing element whose ordinal number as determined bythe LUT is less than P is brought to its first configuration and theremaining pressure producing elements are brought to their secondconfiguration.

A suitable LUT (look up table), which has cells which correspondone-to-one to the N pressure producing elements in the array, storingintegers from 1 to N, may be generated as follows:

A criterion for LUT quality is first determined, which may beapplication-specific. One suitable criterion for LUT quality is nowdescribed.

A list is prepared of all possible subsets of consecutive integersranging between 1 and N. In the present example, the first subset,termed hereinafter S2 ₁, includes 2 integers: 1 and 2; the secondsubset, S2 ₂ includes the integers 2 and 3, and so on for all subsetscontaining two integers. The last two-element subset, S2 ₁₉₉₉₉, containsthe integers 19999 and 20000. The list also includes all possible threeelement subsets, namely, to continue the example, S3 ₁ (which includesintegers 1, 2, 3), S3 ₂ (which includes integers 2, 3, 4), S3 ₁₉₉₉₈(which includes integers 19998, 19999, 20000).

The list also includes all 4 element subsets, 5 element subsets and soon and so forth. The last subset, S20000 ₁ contains all 20000 elements.In general, a subset containing K integers, starting at i is labeledSK_(i). It is appreciated that for a LUT containing N cells, the numberof possible subsets M equals M=(N−1)*N/2.

For each subset SK_(i), a set of coordinates is defined (X_(i), Y_(i)),(X_(i+1), Y_(i+1)), . . . (X_(i+K−1), Y_(i+K−1)) such that thecoordinates represent the position of the pressure-producing elementswhose ordinal numbers are i, i+1, i+k−1 according to the current LUT.

For each subset SK_(i), a propagation angle θK_(i) is computed e.g.using analytic or numeric computation methods, typically using suitablecomputer simulation applications such as Matlab, MatCAD or Mathematica.The sound waves' propagation angles are computed for K coherent soundsources, disposed at positions (X_(i), Y_(i)), (X_(i+1), Y_(i+1)), . . .(X_(i+K−1), Y_(i+K−1)), all producing sinusoidal waves at the same phaseand at a frequency equal to the system sampling rate, e.g. 44100 Hz.

A “propagation angle of a subset” is defined as follows: Each subsetcorresponds to a subset of pressure producing elements. A reference axisis defined passing through the center of mass of the array of pressureproducing elements and perpendicular to its main surface. The intensityof sound generated by the subset of pressure producing elementsapproaches a maximum as one retreats from the array of pressureproducing elements along the reference axis. Therefore, a maximalintensity for the subset may be defined by measuring the intensity at alocation L which is on the reference axis and sufficiently distant fromthe array so as to ensure that the differences between the distance oflocation L and each of the pressure producing elements in the subset aresufficiently, e.g. an order of a magnitude, smaller than the wavelengthassociated with the system clock. At least one reference plane isdefined which includes the reference axis. It is appreciated that aninfinite number of such reference planes exists. For cylindricalpropagation applications in which a focal axis is defined, select areference plane which includes the focal axis. It is appreciated that aLUT constructed on this basis would typically also be suitable foromnidirectional applications. For propagation applications in which afocal point is defined as described herein, select a reference planewhich includes the focal point. If more than one such reference planeexists, select two such reference planes which are mutuallyperpendicular.

The propagation angle of the subset, termed herein θK_(i), is definedfor each reference plane selected for that subset, as follows: Define animaginary circle within the reference plane whose center is at the pointof intersection between the reference axis and the main surface of thearray and whose radius is the distance between L and the main surface ofthe array. Select two locations on the circumference of the circle onboth sides of the reference axis respectively, in which the soundintensity generated by the subset of pressure producing elements is halfof the maximal intensity measured at L. The angle defined between tworadii connecting the center of the circle to these two locationsrespectively is termed the propagation angle of the subset for thatreference plane. If the subset has two perpendicular reference planes asdescribed above, simple or weighted average of the two propagationangles may be computed to obtain a single propagation angle θK_(i) forthe subset. If the directivity pattern across a certain reference plane,e.g. a vertical plane, is more important than that across the other,perpendicular reference plane, greater weight is assigned to the moreimportant plane. For example, in certain applications the most importantconsideration may be to prevent unwanted noise from reaching locationson different floors in which case a vertical reference plane would bemore heavily weighted than the horizontal reference plane.

An example of a suitable criterion for the “best-ness” of a specific LUTis:

LUT _(score)=1/[(average of all θK _(i))×(standard deviation of all θK_(i))]

To determine the most suitable LUT, one may use a computer simulation totest and score all possible permutations i.e. all possible N-cell LUTs,and selecting the best one thereof.

It is appreciated that the number of LUTs, each containing N cells, isN! (N factorial). If N is sufficiently large, it becomes impractical totest and evaluate all possible LUTs i.e. all possible permutations ofintegers into LUT cells. If such is the case, a smaller number of LUTpermutations may be selected, e.g. randomly, and the best one thereof isselected.

It is appreciated that alternatively, step 3200 may be performed withoutresort to a fixed LUT stored during set-up. Instead, the set ofP_(t)-P_(t−1) pressure producing elements to be activated may beselected by selecting the best subset of P_(t)-P_(t−1) elements fromamong the set of pressure producing elements which are currently in thesecond operative configuration. This may be done by estimating thepropagation angle θ for each possible subset of P_(t)-P_(t−1) elementsand selecting that subset which best matches the desired propagationpattern.

P_(t) refers to the current value of P whereas P_(t−1) refers to thevalue of P in the previous system clock.

Furthermore, it is appreciated that in those applications in which thedirectivity pattern is not important, any set of pressure producingelements may be employed to achieve a temporal pressure pattern dictatedby the input signal.

Step 3300, in which the amount of delay with which to operate each ofthe moving elements of moving element array 3010 or 3012 of FIGS.20A-20B, is computed, determines the directionality of the soundgenerated by the speaker. Preferred methods and formulae for optionallypositioning the moving element array as a function of desireddirectionality of propagation, if possible, and for computing delaysalso as a function of desired directionality of propagation, are nowdescribed, for three example propagation patterns termed hereinomni-directional, cylindrical and uni-directional. It is appreciatedthat the three propagation patterns discussed particularly herewithinare discussed merely by way of example.

FIGS. 22A-22B, taken together, describe a simplified example of asolution for performing step 3300 when it is desired to achieveomni-directional sound i.e. sound which propagates outward through threedimensional space from a given point location termed herein the “focalpoint” of the omni-directional sound. Specifically, FIG. 22A is asimplified diagram of an omni-directional propagation pattern having afocal point 3400 and FIG. 22B is a diagram of a preferred positioning ofa moving element array relative to the focal point of the desiredomni-directional sound propagation pattern of FIG. 22A. In theillustrated embodiment, the array of moving elements referencedgenerally 3010 or 3012 in FIGS. 20A-20B comprises, merely by way ofexample, a typically non-skewed array 3410 of 14×21 moving elements. Asshown, the array of moving elements is preferably although notnecessarily positioned, as illustrated in FIG. 22B, such that itsgeometric center (located between the 7^(th) and 8^(th) rows, at the11^(th) column) of the array of moving elements coincides with the focalpoint 3400 of the omni-directional pattern, located at the center of theconcentric circles representing the omni-directional pattern as shown inFIG. 22A. The center of the array may also be positioned at theprojection of the focal point of the omni-directional pattern onto theplane of the moving element array 3410. It is appreciated that the arrayneed not be positioned as illustrated and may instead be positioned atany suitable location, such as a fixed location independent of theparticular propagation pattern currently selected by a user.

It is appreciated that the array need not be of the specified dimensionsor shape. In fact preferred embodiments of direct digital speakers arecomprised of thousands to hundreds of thousands of pressure-producingelements. The shape of the array may change according to applicationand/or use.

It is also appreciated that the focal point referred to herein need notbe positioned on the main surface defined by the array ofpressure-producing elements. Changing the distance between the focalpoint and the main surface of the array of the pressure-producingelements changes the directionality pattern of the device. E.g. placingthe focal point on the surface (zero distance) would produce trueomni-directional directivity pattern where sounds intensity remainessentially equal regardless of the angle in which the sound propagates.Placing the focal point at a certain distance, d behind the surface ofpressure-producing elements defines a projection cone (in the case of around array) or a projection pyramid (in the case of a square orrectangular array) that is characterized by a head angle narrower than180 degrees. Placing the focal point at an infinite distance behind themain surface of the pressure producing elements (given that the soundproduced by the pressure producing elements is produced in front of themain surface) typically defines a projection cone or a projectionpyramid that is very narrow and would produce a true unidirectionaldirectivity pattern. Typically, the sound intensity throughout theprojection cone or projection pyramid remains essentially equal whilethe intensity outside the cone or pyramid is significantly lower. It isappreciated that d may be either 0 or infinity in certain applications.In certain applications, d may be determined as a function of a usercontrol.

FIG. 23 is a simplified pictorial illustration of speaker apparatusconstructed and operative in accordance with FIGS. 20A-22B andoperative, e.g. by virtue of having been so programmed, to generateomni-directional sound which is particularly suitable for theenvironment illustrated in FIG. 23 in which consumers of the soundentirely surround the speaker, typically at more than one levelsincluding a ground level and a first floor level as shown.

For applications in which a pre-determined and fixed focal point ofomni-directional sound propagation is known, e.g. in a conventionalplanetarium, circus arena or circular auditorium, the array of movingelements provided in accordance with certain embodiments of the presentinvention is preferably although not necessarily positioned such thatthe array's center coincides with the desired focal point of the desiredomni-directional propagation pattern as described above with referenceto FIGS. 22A-22B. It is appreciated, however, that although it ispreferable to position the array of moving elements such that its centeris disposed as close as possible to a currently desired e.g.user-selected focal point of a currently desired e.g. user selectedomni-directional propagation pattern, nonetheless, embodiments of theinvention shown and described herein allow omni-directional propagationfrom a wide variety of foci to be achieved using an array of movingelements which may be stationary and need not be centered at the focalpoint of the omni-directional directivity pattern.

Referring back to FIG. 22A, each circle shown represents half a phaseand has a radius r which is computed using the following formula:

r=(Ndλ/2+N ²λ/4)^(0.5)

where: N=the serial number of the circle, counting outward from thecenter and starting from 1,

d=the distance of the plane of the non-skewed array from the focal pointof the omnidirectional sound

λ=c T, where c=the speed of sound through the medium in which thespeaker is operating, typically air, and T=the period of the systemclock of FIG. 20A or 20B (not shown).

It is appreciated that specific delay values for the moving elements inarray 3410, suitable for achieving the omni-directional pattern of FIG.22A, may be determined as follows:

(a) Any moving element which coincides with a circle whose serial numberis N is assigned a delay value of N T/2.

(b) Any moving element which does not coincide with a circle, andinstead falls between a pair of circles whose serial numbers are N andN+1 is assigned a delay value by interpolating e.g. linearly between thefollowing two values: NT/2 and (N+1)T/2.

Alternatively, a suitable formula for determining delays is described indetail below.

FIG. 24 is a diagram of a cylindrical pattern of sound directivity whichit is achievable using an embodiment of the apparatus of the presentinvention. As shown, at each point along the sound propagates, in theplane, omni-directionally and identically from each point along a givenfocal axis 3510.

FIG. 25 is a diagram showing one preferred positioning of the movingelement array 3010, shown to be rectangular by way of example, relativeto the cylindrical pattern of sound directivity shown in FIG. 24. Ifpossible, the moving element array is preferably disposed symmetricallyabout the focal axis such that, as shown, its sides are respectivelyperpendicular to or parallel to the focal axis, or, less preferably andas illustrated, the moving element array is preferably disposedsymmetrically about the projection of the focal axis upon the planedefined by the array. It is appreciated that the particular positioningsdescribed herein and illustrated need not be provided and alternatively,the moving element array may be disposed and oriented in any suitable,application-dictated location.

FIG. 26 is an isometric view of the moving element array 3010 or 3012 ofFIGS. 20A-20B, showing uni-directional sound generated by that movingarray and propagating in a desired or predetermined direction α asindicated by arrows.

FIG. 27 is a pictorial illustration of a preferred application forspeaker apparatus 3600 constructed and operative in accordance with thepresent invention, being constructed e.g. programmed to generateuni-directional sound in at least one typically user-selected direction.In the embodiment of FIG. 27, either or both of two uni-directionalsounds streams 3610 and 3620 are generated to serve listeners located atpositions 3630 and 3640 respectively.

If the array of moving elements is a rectangle 3650 having first andsecond internally parallel and mutually perpendicular pairs of sides,then the array is typically oriented such that the projection of thedesired direction of propagation onto the plane of the array, which maybe vertical as shown in FIG. 27, is parallel to one of the pairs ofsides and hence perpendicular to the other pair of sides as shown inFIG. 26. In this case, the delay of each moving element in the array maybe the product of cos alpha (where alpha is the angle of propagation asshown in FIG. 22) and the distance x of that moving element from aselected one of the pair of perpendicular sides.

As suggested by FIG. 27, it may be desired to produce two sound streamsto be perceived exclusively and simultaneously by listeners positionedin two respective azimuthal positions relative to the speaker, is nowdescribed. According to this embodiment, some of the moving elements inthe array are devoted to producing the first sound stream, and theremaining elements in the array are devoted to producing the secondsound. The delays used for each moving element are determined asdescribed above in the uni-directional case. It is appreciated that moregenerally, any suitable number of sound streams rather than just twosound streams may be produced.

The uni-directional embodiment illustrated in FIG. 26 or 27 has a widevariety of applications, such as but not limited to (a) entertainmentcontent providers, such as television, computer, music player or radio,including a programmable directional speaker operative to senduni-directional sound exclusively to one or more user-selecteddirections. Different content, such as a plurality of language versionscorresponding to a single visual content item, can be sentsimultaneously to a plurality of user-selected directions, thereby toenable a group of friends or family members to share a viewingexperience but to simultaneously and exclusively receive individualizedaudio content, e.g. to each in his own language, corresponding to theviewing experience; and (b) Sound-producing toys including a sensoroperative to monitor the azimuthal and elevational position of the childrelative to the toy and a directional speaker operative to senduni-directional sound exclusively toward the child in a direction whichcorresponds to the child's current azimuthal and elevational positionrelative to the toy.

Generally, a suitable formula for determining a suitable amount of delayfor each moving element, for omni-directional sound propagation, is asfollows:

delay=[(d ² +r ²)^(0.5) −d]/c

where

r=distance between the projection of the focal point onto the movingelements array

plane and a given moving element,

d=the distance of the plane of the array of the moving elements from thefocal point of the omni-directional sound

c=the speed of sound through the medium in which the speaker isoperating, typically air.

For cylindrical sound propagation, the same formula may be employed,however d is now defined as the distance of the plane of the array ofmoving elements from the focal axis which is typically parallel thereto

For unidirectional sound propagation, as described above, the formulaemployed may be

delay=x cos α

where:

x=the distance from the moving elements array edge plane and a givenmoving element and

α=the angle between direction and moving elements array plane.

It is appreciated that the embodiments shown and described hereingenerate sound propagation patterns which well approximate desiredpatterns such as omni-directional, cylindrical, and uni-, bi- or evenmulti-directional patterns. However, at least due to the finite size ofthe array of moving elements, the actual sound propagation pattern isnever exactly identical to the theoretically desired propagationpattern. Generally, the theoretically desired propagation pattern isbetter achieved at locations which are close to the moving elementarray, than at locations which are further from the moving elementarray.

It is also appreciated that the larger the array (both in terms ofnumber of pressure-producing elements and in terms of dimensions), themore closely the desired propagation pattern is achieved.

A particular feature of certain embodiments of the present invention isthat a single speaker including one or more pressure-producing elementarrays which arrays may be fixed, can be programmed to generate aplurality of directivity patterns differing in parameterization or evenin shape.

It is appreciated that a multi-unidirectional propagation pattern may beprovided, in which the user ean, if desired, select the number of and/ordirection and/or other characteristics of more than one uni-directionalbeams. The uni-directional embodiment is described herein andgeneralization of the uni-directional embodiment described herein to amulti-unidirectional embodiment may be achieved using techniques knownin the art such as techniques used to define the direction, number of,and/or other characteristics of beam/s produced by multi-beam phasedarray applications e.g. RADAR beams. More generally, it is appreciatedthat a combination of propagation patterns may be provided, in which theuser can, if desired, select the number of and/or direction and/or othercharacteristics of more than one component propagation patterns each ofwhich may comprise any suitable pattern such as but not limited to auni-directional pattern, omni-directional pattern, cylindrical pattern,or any combination thereof. Several propagation patterns are describedherein and combination thereof may be achieved using techniques known inthe art such as techniques used to define the direction, number of,and/or other characteristics of beam/s produced by multi-beam phasedarray applications e.g. RADAR beams

It is appreciated that the array of moving elements need not be planaras illustrated and that alternatively the teachings of the presentinvention may be appropriately modified to accommodate a non-planararray of moving elements.

FIG. 28 is a simplified pictorial illustration of a non-rectangulararray of moving elements. According to one embodiment of the presentinvention, delays for moving elements in non-rectangular arrays may becomputed by circumscribing the non-rectangular array in a rectangulararray and proceeding to compute delays as described herein, for thecircumscribing rectangular array. Each moving element in thenon-rectangular array is assigned a delay value which equals the delayvalue computed by this process, i.e. according to its position in the(imaginary) circumscribing rectangular array.

If the array of moving elements is not rectangular, the following rulesmay be employed to position the array although alternatively theinvention may accommodate an array of moving elements positionedarbitrarily:

i. If omni-directional propagation is desired and the designer isentirely free to position the array, the array may be positioned suchthat the center of mass of the non-rectangular array coincides with thefocal point of the omni-directional propagation. Preferably and moregenerally, the array may be positioned such that the center of mass ofthe non-rectangular array is as close as possible to the focal point ofthe omni-directional propagation

ii. If cylindrical propagation is desired and the designer is entirelyfree to position the array, the array may be positioned such that anaxis of mass 3700 of the non-rectangular array 3710, partitioning thearray into two sub-arrays 3720 and 3730 of equal area as shown in FIG.28 is disposed along the focal axis of the cylindrical propagation. Ifseveral axes of mass exist, the longest such axis is typically selected.Preferably and more generally, the array may be positioned such that anaxis of mass, preferably the longest available, of the non-rectangulararray is disposed parallel to the focal axis of the cylindricalpropagation.

iii. If uni-directional propagation is desired and the designer is freeto position the array, the array may be positioned such that the desiredpropagation direction is close to perpendicular to the main surface ofthe array.

The scope of the present invention includes but is not limited to amethod for controlling direct digital speaker apparatus receiving adigital input signal and generating sound accordingly, the methodcomprising providing an array of pressure-producing elements, andcomputing a timing pattern determining if and when eachpressure-producing element is operative to produce pressure pulses so asto achieve a desired directivity pattern. The array is then operated inaccordance with the timing pattern in order to achieve sound having thedesired directivity pattern.

Optionally, the providing and computing steps are performed a pluralityof times thereby to obtain a corresponding plurality of arrays and acorresponding plurality of timing patterns defining a correspondingplurality of directivity patterns. The method then also comprises thestep of operating the plurality of arrays simultaneously in accordancewith the corresponding plurality of timing patterns respectively therebyto obtain a single directivity pattern comprising a combination of thedirectivity patterns corresponding to the plurality of timing patterns.The plurality of arrays may in fact comprise portions of a single largerarray. So, for example, a single array of pressure producing elementssuch as any of those shown and described herein may be partitioned intoregions, e.g. quarters, and the pressure producing elements in eachregion may be operated in accordance with its own particular timingpattern or delay pattern. For example, this allows a pattern of several,say four, different unidirectional beams to be achieved. Alternatively,to give another example, this allows, say, omnidirectional backgroundsound to be superimposed on one or more different foreground soundstreams each respectively having its own, say, uni-directional,cylindrical or omni-directional propagation pattern. It is appreciatedthat in multi-directional embodiments, each said unidirectional beam mayproduce a different digital input signal, e.g. the left and rightchannels of a stereophonic signal.

It is appreciated that the electromagnetic field controller 30 ispreferably designed to ensure that the alternating current flowingthrough the coil maintains appropriate magnetic field strength at alltimes and under all conditions so as to allow sufficient proximitybetween the moving elements 10 and the electrostatic latches 20 toenable latching, while preventing the moving elements 10 from moving toofast and damaging themselves or the latches 20 as a result of impact.

With specific reference to the Figures, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of the preferred embodiments of the present invention only,and are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the invention. In this regard, no attempt is madeto show structural details of the invention in more detail than isnecessary for a fundamental understanding of the invention. Thedescription taken with the drawings makes apparent to those skilled inthe art how the several forms of the invention may be embodied inpractice.

Features of the present invention which are described in the context ofseparate embodiments may also be provided in combination in a singleembodiment. Conversely, features of the invention which are describedfor brevity in the context of a single embodiment may be providedseparately or in any suitable subcombination. For example, movingelements may be free floating, or may be mounted on filament-likeflexures or may have a surrounding portion formed of a flexiblematerial. Independently of this, the apparatus may or may not beconfigured to reduce air leakage therethrough to as described above.Independently of all this, the moving element may for example comprise aconductor, coil, ring- or disc-shaped permanent magnet, or ring- ordisc-shaped ferromagnet and the magnets, if provided, may or may not bearranged such that the poles of some e.g. 50% thereof are oppositelydisposed to the poles of the remaining e.g. 50% of the magnets.Independently of all this, the latch shape may, in cross-section, besolid, annular, perforated with or without a large central portion, ornotched or have any other suitable configuration. Independently of allthis, control of latches may be individual or by groups or anycombination thereof. Independently of all this, there may be one or morearrays of actuator elements which each may or may not be skewed and thecross-section of each actuator element may be circular, square,triangular, hexagonal or any other suitable shape.

The present invention has been described with a certain degree ofparticularity, but those versed in the art will readily appreciate thatvarious alterations and modifications may be carried out to include thescope of the following Claims:

1-67. (canceled)
 68. Direct digital speaker apparatus receiving adigital input signal and generating sound accordingly, the apparatuscomprising: an array of pressure-producing elements; and a controlleroperative to compute a timing pattern determining if and when eachpressure-producing element is actuated so as to achieve a desireddirectivity pattern.
 69. Apparatus according to claim 68 wherein eachsaid pressure-producing element is operative to produce both positivepressure pulses and negative pressure pulses.
 70. A method forcontrolling direct digital speaker apparatus receiving a digital inputsignal and generating sound accordingly, the method comprising:providing an array of pressure-producing elements, and computing atiming pattern determining if and when each pressure-producing elementis operative to produce pressure pulses so as to achieve a desireddirectivity pattern.
 71. Apparatus according to claim 68 wherein eachpressure-producing element comprises a moving element, operating totravel alternately back and forth along a respective path.
 72. Apparatusaccording to claim 68 and also comprising a user interface receiving adesired directivity pattern from a user.
 73. Apparatus according toclaim 68 wherein said directivity pattern is omni-directional defining afocal point.
 74. Apparatus according to claim 68 wherein saiddirectivity pattern is cylindrical defining a focal axis.
 75. Apparatusaccording to claim 68 wherein said directivity pattern is unidirectionaldefining an angle of propagation.
 76. Apparatus according to claim 68wherein said directivity pattern comprises a combination of a pluralityof unidirectional directivity patterns.
 77. Apparatus according to claim73 wherein said array is centered at said focal point.
 78. Apparatusaccording to claim 73 wherein said array is centered at a projection ofsaid focal point.
 79. Apparatus according to claim 74 wherein said arrayis oriented symmetrically relative to said axis.
 80. Apparatus accordingto claim 74 wherein said array is rectangular, defining four sidesthereof, and said four sides include two sides parallel to said axis.81. Apparatus according to claim 73 wherein said array defines a planeand wherein said timing pattern comprises employing a suitable delay forat least some of said pressure-producing elements, using the formula:delay=[(d²+r²)^(0.5)−d]/c, where r distance between the projection ofthe focal point onto the array of pressure-producing elements and agiven pressure-producing element, d=the distance of the plane of thearray of the pressure-producing elements from the focal point, and c=thespeed of sound propagation through a medium in which the apparatus isoperating.
 82. Apparatus according to claim 74 wherein said arraydefines a plane and wherein said timing pattern comprises employing asuitable delay for at least some of said pressure-producing elements,using the formula: delay==[(d²+r²)^(0.5)−d]/c, where r distance betweenthe projection of the focal axis onto the array of pressure-producingelements and a given pressure-producing element, c=the speed of soundthrough a medium in which the apparatus is operating, and d=the distanceof the plane of the array of pressure-producing elements from the focalaxis.
 83. Apparatus according to claim 75 wherein said timing patterncomprises employing a suitable delay for at least some of saidpressure-producing elements, using the formula: delay=x cos α wherex=the distance from a plane defined by an edge of the array ofpressure-producing elements and a given pressure-producing element andα=the angle between a direction defined by the uni-directionalpropagation and said plane.
 84. Apparatus according to claim 68 whereineach of said pressure-producing elements is individually controlled. 85.Apparatus according to claim 68 wherein each pressure producing elementis responsive to alternating magnetic fields and wherein the apparatusalso comprises at least one latch operative to selectively latch atleast one subset of said pressure producing elements in at least onelatching position thereby to prevent at least said subset of pressureproducing elements from responding to said alternating magnetic fields,and wherein said controller comprises: a magnetic field control systemoperative to receive a clock and, accordingly, to control application ofsaid alternating magnetic fields to said array of pressure producingelements; and a latch controller operative to receive said digital inputsignal and to control said at least one latch accordingly.
 86. A methodaccording to claim 70 wherein said array providing and said computingare performed a plurality of times thereby to obtain a correspondingplurality of arrays and a corresponding plurality of timing patternsdefining a corresponding plurality of directivity patterns; the methodalso comprising operating said arrays simultaneously in accordance withsaid corresponding plurality of timing patterns respectively thereby toobtain a single directivity pattern comprising a combination of thedirectivity patterns corresponding to said plurality of timing patterns.87. Apparatus according to claim 68 wherein said elements moveharmonically and have a single amplitude and a single frequency.